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Topography of the digital cutaneous sensilla of the tokay gecko, Gekko gecko (Reptilia, Gekkonidae), and their potential role in locomotion
Abstract and Figures
The external morphology of the cutaneous sensilla of the dorsal digital scales of the tokay gecko, Gecko gecko, is described and the distribution of the various sensillar types is mapped. Three types of sensilla are identified: bristleless, bristled unbranched, and bristled branched. Bristleless sensilla occur only on glabrous scales and are largely restricted to the toe base and phalangeal scales. They may register stimuli other than those associated with scale-to-scale contact. Bristled unbranched sensilla are recessed and are located on the paralamellar, phalangeal, paraphalangeal, and toe base scales, but the bristled branched variety is largely restricted to the paraphalangeal region. The mechanoreceptive role of the bristle-bearing sensilla is related to their placement on individual scales and their distribution across the digit. Placement of the sensilla accords well with patterns of scale-to-scale and scale-to-substrate contact that occur during digital hyperextension and plantarflexion. Such proprioceptive monitoring of regions of the digit during locomotion may be of considerable significance in the control of the establishment and sundering of the adhesive bond that occurs between the setae and the locomotor substrate.
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... Geckos are a particularly speciose and diverse clade of squamates, which have relatively thin and soft skin compared to other reptiles (Boulenger, 1885, p. 5), typically covered with cutaneous sensilla (Bauer & Russell, 1988;Hiller, 1976) and occasionally lenticular sense organs in some species (Riedel et al., 2019). Despite the uniformity of internal structures, cutaneous sensilla in geckos vary considerably in their surface morphology, especially the bristles (Hiller, 1971;Lauff et al., 1993;Riedel et al., 2019;Schleich & Kästle, 1982;Schmidt, 1912). ...
... Cutaneous sensilla are mechanoreceptive (Hiller, 1978), and although the bristles are not innervated themselves, bristle movement triggers a neural reaction through the innervated dermal papilla (Hiller, 1978;von Düring & Miller, 1979). For example, the cutaneous sensilla on the fringes of the adhesive toepads of Tarentola geckos were associated with the placement of the toepads during locomotion (Hiller, 1976) and there are different sensilla morphologies (unbristled, bristled with an unbranched bristle and bristles with a split tip) on different regions of the dorsal manus and pes of Tokay Geckos (Gekko gecko), another species with adhesive toepads, suggesting that the sensilla may play a role in toepad placement in this species as well (Lauff et al., 1993). In contrast, the sensilla of a padless leopard gecko (Eublepharis macularius) were uniform across all body regions except for the labials (Russell et al., 2014). ...
... We determine if sensilla morphology is uniform across body regions. We expect that, consistent with some other species (Bauer & Russell, 1988;Lauff et al., 1993), sensilla morphology may differ among the tail, head and feet of geckos. Next, we quantify sensilla number and distribution among body regions and species. ...
Skin sense organs, i.e., cutaneous sensilla, are a well‐known feature of the integument of squamate reptiles, and particularly geckos. They vary widely in morphology among species, and are thought to be mechanosensitive, associated with prey capture and handling, tail autotomy, and placement of the adhesive toepads in pad‐bearing species. Some authors suggest that they may also sense abiotic environmental features, such as temperature, or humidity. Here, we describe the morphology and distribution of cutaneous sensilla among body regions of nine Australian gecko species, in four genera. We hypothesised that if sensilla morphology was distinct, or sensilla density high, around the mouth, on the tail, and on extremities, sensilla were likely used for these direct tactile functions. We found that sensilla morphology was uniform among body regions within species, but varied among species, while sensilla densities varied among species and body regions. In gecko species studied, sensilla density was highest on the labials and the dorsal tail scales, and low on the feet, head and body, providing strong support for the hypothesis that sensilla serve tactile mechanoreceptive functions for prey capture and handling and for predator avoidance, but not for toepad placement. We suggest sensilla density may be explained by mechanoreception, whereas structure may be influenced by other factors.
... That similarity was expressed in spatial distribution and sizes of MiO spinules on the scale surface, and in the small size, external and inner morphology of SSO, including the sizes, diversity and composition of their hairs and hair inner structure (Tables 3 and 4; Schmidt, 1913Schmidt, , 1920Ruibal, 1968;Hiller, 1971;Joger, 1984;Dujsebayeva, 1995;Röll, 1995;Nikitina and Ananjeva, 2005;Darvish, 2012;Alibardi and Bonfitto, 2019;Riedel et al., 2019). We only failed to find sensory organs with bifurcated hairs, as occurs in some geckos (Sammartano, 1980;Bauer and Russell, 1988;Lauff et al., 1993) as well as the sensory organs like tufts of villi described by Underwood (1957) for some pygopods. ...
... A singularity of SSO of Australian geckos of the family Carphodactylidae -Nephrurus, Phyllurus, and Underwoodisaurus bearing thick hairs with setules throughout its length (Russell and Bauer, 1987;Bauer and Russell, 1988;Riedel et al., 2019) does not go beyond the general morphogenetic potency of the Oberhäutchen cells to pro-duce the folds. A fundamentally similar pattern with setules scattered along the hairs of SSO also occurs in the gecko Gekko gecko (Lauff et al., 1993) and Gonuisaurus luii (Koppetsch et al., 2020), at the base of simple spinules of MiO in iguana A. carolinensis (Maderson et al., 1998: Fig. 10) and even on the hairs of SSO in acrochordid sea snake A. javanicus (Povel and Kooij, 1997). Resurrecting the term "Oberhäutchen multi-hair organ" proposed by Williams (1988: p. 451), we suggest that the gekkotan, dactyloid, oplurid and chameleonid SSO with their corneous outgrowths derived from MiO be called "Oberhäutchen hairy sensory organs" (ObHSO) meaning by the term "hair" specifically the enlarged derivatives of the Oberhäutchen cell surface. ...
... These lizards possess only lenticular sensory organs of large or medium sizes (Table 4) and lack any corneous outgrowths (Scortecci, 1940;Williams, 1988, personal communication;Ananjeva et al., 1991). Lauff et al. (1993) wrote that the "...the autarchoglossan squamates… lack a spinulate scale microarchitecture..." (p. 2468). ...
The skin, as the interface of the body with the outside world, is directly exposed to the impacts of the environment. We have examined the microstructure of scale surfaces and the numerical distribution and morphology of skin sensory organs (SSO) in Australian limbless lizards of the family Pygopodidae. We have shown that the hairy sensory organs, as complex morphological structures, are a stable characteristic of the scale integument of pygopodids. This feature reflects their relationship to geckos and is shared homoplastically with some iguanian families (Dactyloidae, Leiosauridae, Opluridae, Chamaeleonidae). At the same time, scale micro-ornamentation as an elementary morphological structure is more plastic and, although the basic spinulate pattern is dominant, other variants occur on the scales of the serpentine body of pygopodids. We accept the spinules of MiO and the hairs of SSO as homologous structures at the cellular level since they are both derivatives of the Oberhäutchen cell surface. We propose to characterize the hair-bearing SSO of gekkotan and iguanian lizards as Oberhäutchen hairy sensory organs (ObHSO). Domination of SP MiO and presence of ObHSO in the integument of Gekkota and several families of Iguania, and sporadic occurrence of SP MiO in autarchoglossan taxa provide justification for regarding these characters as plesiomorphic. We characterize the high abundance (iterative state) of SSO in the scales of the head of pygopodids as representing the phenomenon of «overiteration», in which the phylogenetically established condition is enhanced by functional demands on the organism.
... Gourvest (1960) found that the dorsal and lateral scales of the toes of Tarentola mauritanica generally bear bristleless cutaneous sensory organs on their distal margins. Lauff et al. (1993) described the distribution of both bristleless and bristle-bearing organs on the digits of Gekko gecko and noted that those on the dorsal digital surface of the Tokay gecko vary in position and form. They correlated this with functional specialization. ...
... In Gekko gecko bristled unbranched cutaneous sensory organs are found on the paralamellar, phalangeal and the more lateral of the paraphalangeal scales (Lauff et al., 1993: Fig. 10) of the toepad, as well as on the toe base, whereas bristled branched cutaneous sensory organs are largely restricted to the more medial of the paraphalangeal scales in the region of the toepad. Lauff et al. (1993) showed that the moderately-recessed, bristled unbranched cutaneous sensory organs on the dorsal phalangeal and paraphalangeal digital scales have their bristles oriented to maximize the possibility of being impinged upon by adjacent scales during the process of digital hyperextension. On certain scale rows cutaneous sensory organs are located only in areas where the proximal end of the abutting scale would make contact upon hyperextension. ...
... On certain scale rows cutaneous sensory organs are located only in areas where the proximal end of the abutting scale would make contact upon hyperextension. Lauff et al. (1993) hypothesized that differentially positioned and constructed cutaneous sensory organs may be of significance in registering different degrees of distortion of the toepad. ...
Cutaneous sensory organs are characteristic of many squamate lineages. Such organs may occur on the surface of scales as button-like, circular protuberances set off from their surroundings by a noticeable boundary, often taking the form of a moat or furrow. They may be relatively unadorned, clad with the surface micro-ornamentation of the scales on which they are carried, or they may carry one or more bristles of varying length and surface ornamentation. Such bristles may extend away from the body of the organ to interface with the surrounding environment or to contact adjacent scales. Cutaneous sensory organs have been physiologically demonstrated to have a mechanoreceptive function but have also been posited to potentially be involved with additional sensory modalities. Their distribution and structure across the body surface has been shown to be unequal, with some regions being much more extensively endowed than others, indicative of regional differential sensitivity. The digits of Anolis (Iguania: Dactyloidae) carry adhesive toepads that are convergent with those of geckos (Gekkota). Geckos exhibit a high density of cutaneous sensory organs on their toepads and their form and distribution has been associated with the operation and control of the toepads during locomotion. Investigation of the form and topographical distribution of cutaneous sensory organs on the toepads of Anolis shows them to be convergent in these attributes with those of geckos and quite distinct from those of the ancestrally padless Iguana (Iguania: Iguanidae). Their location at scale margins and the direction of their bristles towards adjacent scales indicates that the cutaneous sensory organs play an important role in proprioception during toepad deployment in Anolis.
... Gecko skin also features mechanoreceptors, called cutaneous sensilla (Hiller, 1976;Bauer & Russell, 1988). For example, the distribution and form of cutaneous sensilla on the dorsal surface of the feet of the Tokay gecko (Gekko gecko) aid in the correct placement of the toes to maximise adhesive toe pad function (Lauff et al. 1993). Also, the density and distribution of cutaneous sensilla on the tail of the leopard gecko (Eublepharis macularius) suggests that they mediate the location of tail breakage and the movement of the tail after breaking (Russell et al. 2014). ...
... Dorsal epidermal scale moulds were taken from the mid-dorsal region halfway between the front and the hind limbs, because Mt. Isa, QLD (20°49 0 30″ S, 139°27 0 42″ E) Arboreal Mesic microstructures (especially cutaneous sensilla) in this area may be less likely to perform specialised functions such as detecting body movement or posture, tail breakage or prey capture (Lauff et al. 1993;Russell et al. 2014). Detailed epoxy-resin moulds of live specimens were made according to methods described by Vucko et al. (2008). ...
... Multiple bristles per sensillum also occur in the pygopodid genus Lialis (Spinner et al. 2013a) and are widespread but sporadic within the Gekkomorpha (Schmidt, 1912;Hiller, 1976;Ananjeva et al. 1991;Duisebayeva, 1995;Nikitina & Ananjeva, 2003;Yonis et al. 2009;Darwish, 2012;Russell et al. 2014). Lauff et al. (1993) described bristleless sensilla and sensilla with branched bristles cooccurring, with simple, unbranched bristles on the feet of Gekko gecko. Thus, different sensilla morphologies occur even within a single species, although our findings suggest that sensilla morphology does not vary on the dorsal surface. ...
A first step in examining factors influencing trait evolution is demonstrating associations between traits and environmental factors. Scale microstructure is a well‐studied feature of squamate reptiles (Squamata), including geckos, but few studies examine ecology the of microstructures, and those focus mainly on toe pads. In this study, the ecomorphology of cutaneous microstructures on the dorsum was described for eight Australian species of carphodactylid (Squamata: Carphodactylidae) and 19 diplodactylid (Squamata: Diplodactylidae) geckos. We examined scale dimensions, spinule and cutaneous sensilla (CS) morphology, using scanning electron microscopy, and described associations of these traits with microhabitat selection (arboreal, saxicoline or terrestrial) and relative humidity of each species’ habitat (xeric, mesic or humid). We used a phylogenetic flexible discriminant analysis (pFDA) to describe relationships among all traits and then a modeling approach to examine each trait individually. Our analysis showed that terrestrial species tended to have long spinules and CS with more bristles, saxicoline species larger diameter CS and arboreal species tended to have large granule scales and small intergranule scales. There was high overlap in cutaneous microstructural morphology among species from xeric and mesic environments, whereas species from humid environments had large diameter CS and few bristles. Significant associations between epidermal morphology and environmental humidity and habitat suggest that epidermal microstructures have evolved in response to environmental variables. In summary, long spinules, which aid self‐cleaning in terrestrial geckos, are consistent with greater exposure to dirt and debris in this habitat. Long spinules were not clearly correlated to environmental humidity. Finally, more complex CS (larger diameter with more bristles) may facilitate better perception of environmental variation in geckos living in drier habitats.
... There have been occasional reports of bifid bristles (Table 2) in gekkonid genera (Hemidactylus turcicus- Sammartano, 1980; C. laevigatus and Pachydactylus rangei- Sammartano, 1983), taxa for which we also record this characteristic (Table 3). Lauff et al. (1993) noted the presence of sensilla with both unbranched and bifid bristles on the dorsal digital scales of G. gecko and reported that they showed differential and complimentary patterns of distribution, suggestive of regionally based functional differences. The actual functional role of bifid versus unbranched sensilla remains entirely unknown, however. ...
... Such approaches can be combined with assessments of the density of sensilla, as measured by the number of these structures per scale (Dujsebayeva et al., 2021) or within a specified area (e.g., per square millimeter) of the integument (Lauff et al., 1993;Russell et al., 2014;Riedel et al., 2019). Only by more focused approaches, such as those outlined above, can potential relationships between sensillar form, density, and function begin to be deduced. ...
Cutaneous sensory organs (sensilla) are mechanoreceptive structures present in the skin of squamate reptiles. In gekkotan lizards these structures are characterized by a raised eminence, the button, which bears one or more elongate hair-like bristles as well as a field of shorter spinules. Variation in the dimensions of these structures and in the number and elaborations of the bristles have been well characterized in the limbless pygopodid gekkotans and their tetrapodal relatives in the Diplodactylidae and Carphodactylidae, but patterns of variation in the Gekkonidae, by far the most diverse and species-rich clade of gekkotans, remain unexplored. We used scanning electron microscopy to examine and characterize the sensilla of 47 species representing 11 major clades of gekkonids, as well as representatives of other gecko families. Variation in morphology across gekkonid sensilla exceeds that observed in other gecko families, with bristle number varying from zero to 29 and bristle length from 3 to 50 lm.
There is some phylogenetic signal in sensillar morphology, particularly within genera, but there is no association between mechanoreceptor dimensions and overall body size. In some taxa there is evidence that bristle length and bristle number are inversely related. Intraspecific variation in receptor size and configuration, both between individuals and across different body regions, is clearly present but remains insufficiently documented.
... Russell (2002) documented many of the hierarchically integrated mechanical units (sensu Gans, 1969) of its digital adhesive apparatus and discussed how these are coordinated to bring about effective substratum contact and release of the setal arrays. Lauff et al. (1993) provided information about cutaneous sensilla on the Tokay's digits, thereby indicating how sensory feedback is inculcated into the operation of the adhesive apparatus. ...
The modes and mechanisms of organismal attachment are numerous and diverse. Terrestrial vertebrates, however, achieve robust and releasable attachment to both abiotic and biotic substrata in three chief ways: hook-like anchors, such as claws, permit temporary attachment to surfaces via mechanical interlocking and/or frictional interactions with surface asperities; attachment organs releasing glandular secretions (e.g., the toe pads of hylid frogs, suction cups of disc-winged bats) achieve attachment via wet adhesion and/or suction; subdigital pads of some lineages of lizards possess filamentous outgrowths that induce friction and/or adhesion via molecular interactions. Lizards are the largest organisms to employ fibrillar-based attachment, but only the adhesive subdigital pads of geckos and anoles are sufficiently adhesively competent to support forces in excess of their body mass. The adhesive systems of geckos and anoles have long been considered convergent, but beyond general statements to this effect, convergence has not been rigorously assessed. Here we review what is known of the adhesive apparatus of both gekkotan and anoline lizards within the context of two hierarchically stratified domains: (1) adhesive attachment and the structure of setae and setal fields, and (2) the higher-order anatomical specializations that control the operation of the setae. We employ this information to identify the physical and organismic drivers of convergence of fibrillar adhesive systems, thereby enabling us to assess the particular, rather than superficially general, extent of convergence of the adhesive system of geckos and anoles. Our synopsis of gekkotan and anoline setae, setal fields, and their adhesive systems reveals numerous physical and organismic constraints, perceived as the drivers of convergent evolution, that have led to similar morphological and functional outcomes. We posit that the setae and setal fields of geckos and anoles are convergent structures that enhance effective attachment to diverse substrata. Setae exhibit deep homology, arising from the convergently evolved spinulate Oberhäutchen of the epidermis. Following the initial exaptation of spinules as van der Waals adhesion-promoting setae, those of geckos and anoles followed somewhat different evolutionary pathways as the setae became organized into integrated setal fields. These pathways are reflective of differences in how the biomechanical control of the setal fields, during their application and release from the substratum, is achieved. Although anoles seemingly exhibit only a single evolutionary origin of the adhesive system, that of geckos has arisen on multiple independent occasions, with a broad range of expression of anatomical configurations that characterize the functional system. A broad survey of such configurations among geckos reveals that some are morphologically (and probably behaviorally) more similar to those of anoles than are others. Our assessment of the extent of convergence of the adhesive apparatuses of geckos and anoles identifies gekkotan taxa with an adhesive apparatus that most closely resembles that of anoles and explores what is minimally necessary to promote reversible attachment via molecular interactions. Our findings should contribute not only to ongoing investigations of the functional morphology of these adhesive systems but also should be informative to those who design biomimetic fibrillar adhesives intended to operate similarly to their natural counterparts.
... On the other hand, structure and function of reptile cutaneous mechanoreceptors were deeply investigated using electrophysiological, morphological, histological, and electron-microscopical methods in the years 1960-1970 and beyond [59][60][61][62][63][64][65][66]. At the same time, relatively few works have been written on the innervation and mechanoreceptors of the gecko's toes, and they are mainly devoted to cutaneous sensilla (skin sensory organs) [67][68][69][70][71]. Thus, the role of the nervous system in geckos' adhesion remains deficiently investigated. ...
Spaceflight may cause hypogravitational motor syndrome (HMS). However, the role of the nervous system in the formation of HMS remains poorly understood. The aim of this study was to estimate the effects of space flights on the cytoskeleton of the neuronal and glial cells in the spinal cord and mechanoreceptors in the toes of thick-toed geckos (Chondrodactylus turneri GRAY, 1864). Thick-toed geckos are able to maintain attachment and natural locomotion in weightlessness. Different types of mechanoreceptors have been described in the toes of geckos. After flight, neurofilament 200 immunoreactivity in mechanoreceptors was lower than in control. In some motor neurons of flight geckos, nonspecific pathomorphological changes were observed, but they were also detected in the control. No signs of gliosis were detected after spaceflight. Cytoskeleton markers adequately reflect changes in the cells of the nervous system. We suggest that geckos’ adhesion is controlled by the nervous system. Our study revealed no significant disturbances in the morphology of the spinal cord after the prolonged space flight, supporting the hypothesis that geckos compensate the alterations, characteristic for other mammals in weightlessness, by tactile stimulation.
... Sensilla are widely distributed across the body of most lizards (e.g. Hiller, 1968Hiller, , 1971Matveyeva and Ananjeva, 1995;Russell et al., 2014), and hence are well positioned to participate in proprioception, tactile sensitivity, and the detection substrate-borne vibrations associated with locomotion, predator/prey detection and possibly communication (Lauff et al., 1993;Sherbrooke and Nagle, 1996;Barnett et al., 1999;Russell, et al., 2014; see also Hetherington, 1989;Virant-Doberlet et al., 2019). For example, the fossorial sandfish lizard (Scincus scincus) uses vibrational information to locate prey on or within a sandy substrate (Hetherington, 1989). ...
Amongst tetrapods, mechanoreceptors on the feet establish a sense of body placement and help to facilitate posture and biomechanics. Mechanoreceptors are necessary for stabilizing the body while navigating through changing terrains or responding to a sudden change in body mass and orientation. Lizards such as the leopard gecko ( Eublepharis macularius ) employ autotomy – a voluntary detachment of a portion of the tail, to escape predation. Tail autotomy represents a natural form of significant (and localized) mass loss. Semmes-Weinstein monofilaments were used to investigate the effect of tail autotomy (and subsequent tail regeneration) on tactile sensitivity of each appendage of the leopard gecko. Prior to autotomy, we identified site-specific differences in tactile sensitivity across the ventral surfaces of the hindlimbs, forelimbs, and tail. Repeated monofilament testing of both control (tail-intact) and tail loss geckos had a significant sensitization effect (i.e., decrease in tactile threshold, maintained over time) in all regions of interest except the palmar surfaces of the forelimbs in post-autotomy geckos, compared to baseline testing. Although the regenerated tail is not an exact replica of the original, tactile sensitivity is shown to be effectively restored at this site. Re-establishment of tactile sensitivity on the ventral surface of the regenerate tail points towards a (continued) role in predator detection.
... 1D and 2A) (Russell 1975). These movements are controlled by the muscles of the digits ( Fig. 2A) (Russell 1975), and are likely monitored by cutaneous sensilla in localized patches on the dorsal surface of the digit (Lauff et al. 1993;Röll 1995). The process of hyperextension ( Fig. 2A) (whether distal to proximal or vice versa; Russell and Bels 2001;Higham et al. 2017) likely plays a major role in the deployment and detachment of setae (Fig. 1D), and therefore locomotion (Russell and Higham 2009). ...
Geckos are remarkable in their ability to reversibly adhere to smooth vertical, and even inverted surfaces. However, unraveling the precise mechanisms by which geckos do this has been a long process, involving various approaches over the last two centuries. Our understanding of the principles by which gecko adhesion operates has advanced rapidly over the past 20 years and, with this knowledge, material scientists have attempted to mimic the system to create artificial adhesives. From a biological perspective, recent studies have examined the diversity in morphology, performance, and real-world use of the adhesive apparatus. However, the lack of multidisciplinarity is likely a key roadblock to gaining new insights. Our goals in this paper are to 1) present a historical review of gecko adhesion research, 2) discuss the mechanisms and morphology of the adhesive apparatus, 3) discuss the origin and performance of the system in real-world contexts, 4) discuss advancement in bio-inspired design, and 5) present grand challenges in gecko adhesion research. To continue to improve our understanding, and to more effectively employ the principles of gecko adhesion for human applications, greater intensity and scope of interdisciplinary research are necessary.
Behaviour is shaped by the perception of the surrounding world, which is created by the senses. Reptilian sensory systems are shaped by the varied ecologies and complex evolutionary histories of reptiles. In this chapter, we outline the major senses of reptiles: photoreception (vision, parietal eyes, cutaneous), mechanoreception (hearing, balance, and touch), chemoreception (gustation, olfaction, vomeronasal), thermoreception (cutaneous, heat-pit), and magnetoreception. We give general descriptions of the sensory anatomy, including relevant examples of how senses relate to the behaviour and sensory evolution of these animals. We also focus on how major senses mediate intraspecific communication in reptiles, focusing on visual communication via colouration and other visual displays, acoustic communication through calls and songs, and chemical communication using specialised scent glands. Among the diverse sensory specialisations of reptiles, we also outline some of the rare senses for select taxa including magnetoreception navigation in archosaurs, and heat-pit foraging in snakes. Although these unusual senses can be directly related to important behaviours, reptiles do not rely solely on one sensory system for any behaviour, and almost all stimuli are integrated in the brain to inform immediate decision-making. Thus, all sensory capabilities should be considered when attempting to understand the relative importance of sensory systems to reptilian behaviour. We aim to impart an appreciation for how different stimuli may be perceived by reptiles in captivity. Further, signals salient to various reptiles may be invisible to humans (e.g. UV colouration, pheromones), and different reptiles may have heightened or impoverished sensory abilities. Thus, an understanding of reptilian sensory systems is vital for ensuring animal health and welfare in captivity.
The structure and topography of cutaneous receptors of 21 species of iguanian lizards were studied using histology and scanning electron microscopy. Sense organs with "hairs" are found in the integument of Ceratophora, Draco, Phrynocephalus, Stellio, and Trapelus (agamids), and in Anolis, Chalarodon and Oplurus (iguanids). Sense organs without "hairs" are found in the integument of Physignathus (agamid) and Sceloporus (iguanid). The chameleons have generalized epidermal receptors with simplified structure. Familial differences were observed in the numbers of receptors on the scales of the head and the tail: iguanids have 5-7 times more receptors than agamids. Physignathus differs from other agamids in the morphology, size, and number of receptors. These receptors are hypothesized to serve several functions (as mechano- and thermoreceptors, and possibly sensitivity to humidity).
The surface morphology of the cutaneous sensilla of 12 species of carphodactyline geckos is described and discussed in light of sensillar function and the phylogeny of the tribe. Sensilla are common on paralamellar scales of most geckos but are here described for the first time from the scansorial plates themselves in Hoplodactylus maculatus. Sensilla from all members of the New Zealand – New Caledonian lineage of carphodactylines bear a single central bristle. The Australian padless geckos (Nephrurus, Phyllurus, Underwoodisaurus) bear sensilla with one to eight bristles which themselves bear many lateral setules. This state is a synapomorphy of those taxa. The spinose subdigital scales and the scales of the knob-tail of Nephrurus bear sensilla without bristles. The absence of bristles is correlated with the lack of epidermal microarchitecture in Nephrurus (perhaps a paedomorphic feature), and with functional demands that expose the sensilla to constant direct substrate contact.
The microarchitecture of the scale surfaces of Sphenodon punctatus was examined by scanning electron microscopy and compared with the morphologies described for a variety of lizards. The scale surfaces of Sphenodon lack ornamentation, and the epidermal cells have a laminar or lamellate arrangement in which the distal border of one cell overlaps the proximal border of the next distal cell. The cells are moderately elongated perpendicular to the proximo-distal axis of the scale. Among the scale surface morphologies described for lizards, the lamellate arrangement of Lacerta and Gerrhonotus is most similar to the Sphenodon morphology. The lamellate epidermal morphology may be primitive for lizards.
Tactile sense organs in the skin of the head of 42 species belonging to several squamate families are described. These sense organs always consist of a dermal and an epidermal component. Six different types of these sense organs are distinguished. The sloughing cycle of the epidermal component of the sense organs occurs principally in the same manner as it does in the epidermis. The phenomenon of “persisting cells,” which occurs in some families, is discussed. Number and distribution of the organs are not considered.
The digital setae of gekkonids and anoline lizards show free ends which consist of disk-like thickenings, deepened towards their centre. The climbing ability of the reptiles investigated depends mainly on adhesion processes.
The tail of lizards in the Australian gekkonid genus Nephrurus bears a characteristically expanded distal tip, the caudal knob. Anatomical and histological investigation of the knob reveals it to be an integumentary derivative with a massively hypertrophied dermal component. The knob's structure indicates that it is probably used to monitor the environment by detecting mechanical stimuli via the profuse array of sensilla on its surface. The vascular supply to it suggests that the knob may also be involved in thermoregulation.