**3. Reptile groups and their special skin features, especially their scales/ scutes**

The skin of reptiles reflects their greater commitment to a terrestrial existence as mentioned earlier in the chapter. Keratinization is extensive and skin glands are fewer than in amphibians. Scales are present, but these are fundamentally different from the dermal scales of fish. The reptilian scale usually lacks the bony under support or any significant structural contribution from the dermis. Instead, it is a fold in the surface epidermis, hence, an epidermal scale. The junction between adjacent epidermal scales is the flexible hinge (**Figure 1**). If the epidermal scale is large and

#### **Figure 1.**

*Layers of epidermis in reptile skin, consisting of stratum basale (germinal layer) (b), where we find a layer of live cells, and then dead but fully differentiated layers of keratinocytes, which are also named α-layer (c), mesos layer (d), β-layer (e) and Oberhäutchen layer (f). Germinal layer lies on the basal lamina (a) and below lies the tissue of the dermis. Fully differentiated layers are parts of stratum granulosum (intermedial layer) with a stratum corneum, consisting of α-keratin and β-keratin. The junction between epidermal scales is the flexible hinge (adopted from Chang et al. [1] and designed by Pia Cigler).*

plate-like, it is sometimes termed a scute. Additionally, epidermal scales may be modified into crests, spines, or horn-like processes. Although not usually associated with scales, dermal bone is present in many reptiles. The gastralia, a collection of bones in the abdominal area, are examples of these. Where dermal bones support the epidermis, they are called osteoderms, plates of dermal bone located under the epidermal scales. Osteoderms are found in Crocodilians, some lizards, and some extinct reptiles. Some bones of the turtle shell are probably modified osteoderms.

Scales have many important functions, such as playing vital roles in skin permeability and providing protection from abrasion, and therefore tend to be thicker dorsally than ventrally. In some species, they form into large plates and shields on the head. In snakes, they are widened ventrally to form gastropeges, which are important for locomotion [1, 8].

#### **3.1 Lizards and their skin properties**

### *3.1.1 Scales*

The lizard's skin is specific due to scales that form dense tight rows. Lizard scales vary in form from tubercular to plate-like or even largely overlapping each other in formation. The scales originate from the epidermal superficial layer of the skin and form keratinized wrinkles and may have bony plates underlying them (*osteoderms*). They are very close to each other, and links between them allow them to move in all directions. In lizards, scales can vary in form and be modified into crests, spikes, or horns, depending on the type of lizard and on the body part of the lizard and are often of use in taxonomically differentiating species. On the head and on the ventral part, scales are plate-shaped. Scales are important to prevent water loss from the body, as well as to protect the body from injury, because the lizards touch the ground with the ventral surface of the body and thus damage the skin. The skin in the lizard does not follow the growth of the body, so they have to change it, which does not happen in one piece but in several smaller pieces [14].

In some lizards, it is characteristic that their fingers are covered with large scales. These scales serve them to move easier as in the case of the basilisk lizard (*Basiliscus* 

**139**

**Figure 2 .**

*(Photography, Valentina Kubale).*

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

that is also changed in the process of ecdysis.

thermoregulation but also in hormone production [16].

*basiliscus*), especially on the water surface or are helpful in the sand skink (*Neoseps reynoldsi*) to move in the sand. Geckos (Gekkonidae) have flattened fingers, characterized by around 20 leaf-like formations on the ventral side of the toes, named lamellas, with a structure that enables animals to climb on the vertical and very smooth surfaces (**Figure 2**). Lamellas consist of seatae (110 μm in length and 4.2μm in width), which are similarly oriented and uniformly distributed in arrays [14]. Each seta branches to form a nanoarray of hundreds of spatular structures, which are 0.2 μm in length and width at the tip which then make adjacent contact with the surface. Gecko setae are formed primarily of β-keratin with some α-keratin components [15]. The skin glands are mostly restricted to certain parts of the body. Thus, in the medial side of the thighs of many lizards, for example, Green Iguana (*Iguana iguana*), there are femoral pores, beneath which femoral glands are located. These glands are larger and usually more developed in males. They secrete a waxed secretion that contains various pheromones relevant to the mating period or when the animal feels endangered. They also help to determine sex in these species [14]. The lizards do not have an external ear; however, in some species, they have a fold of the skin and tympanic membrane that can be seen from the side on the head in a shallow recess. This membrane is covered by a thin membrane in some species

Some lizards such as Green Iguana (*Iguana iguana*) have partial third eye. This organ is a superficial parietal gland which also contains a lens, cornea, and retina, and is located immediately below the skin in the parietal opening between the parietal and frontal bones. The partial eye is a cavitary organ, which is constructed from epithelial cells that contain secretion glands and photoreceptors that convert light stimuli into neuroendocrine messages that can play an important role in

Lizard skin contains classical skin layers, which can vary in morphology at different positions. Here, we compare skin of the Leopard Gecko (*Eublepharis macularius*)

both sampled from the dorsal region. The most visible difference in the epidermis was seen in the level of keratinization, where the skin of the Green Iguana was keratinized to a higher extent and the outermost β-layer was much more pronounced. The second most prominent feature observed are the melanocytes, where in the Green Iguana the melanocytes are hardly seen at all. On the other hand, Leopard Geckos can vary very much in color and they exist in various color mutations

*The ventral view of a New Caledonian Giant Gecko (Rhacodactylus leachianus) climbing a vertical glass surface. On the ventral view of the foot of a New Caledonian Giant Gecko, a foot adhesive system is observed with adhesive lamellas which consist of microscale array of setae, which are together clustered in tetrads* 

(**Figure 3**) with the skin of the Green Iguana (*Iguana iguana*) (**Figure 4**),

#### *Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

*Veterinary Anatomy and Physiology*

important for locomotion [1, 8].

*3.1.1 Scales*

**Figure 1.**

**3.1 Lizards and their skin properties**

*hinge (adopted from Chang et al. [1] and designed by Pia Cigler).*

plate-like, it is sometimes termed a scute. Additionally, epidermal scales may be modified into crests, spines, or horn-like processes. Although not usually associated with scales, dermal bone is present in many reptiles. The gastralia, a collection of bones in the abdominal area, are examples of these. Where dermal bones support the epidermis, they are called osteoderms, plates of dermal bone located under the epidermal scales. Osteoderms are found in Crocodilians, some lizards, and some extinct reptiles. Some bones of the turtle shell are probably modified osteoderms. Scales have many important functions, such as playing vital roles in skin permeability and providing protection from abrasion, and therefore tend to be thicker dorsally than ventrally. In some species, they form into large plates and shields on the head. In snakes, they are widened ventrally to form gastropeges, which are

*Layers of epidermis in reptile skin, consisting of stratum basale (germinal layer) (b), where we find a layer of live cells, and then dead but fully differentiated layers of keratinocytes, which are also named α-layer (c), mesos layer (d), β-layer (e) and Oberhäutchen layer (f). Germinal layer lies on the basal lamina (a) and below lies the tissue of the dermis. Fully differentiated layers are parts of stratum granulosum (intermedial layer) with a stratum corneum, consisting of α-keratin and β-keratin. The junction between epidermal scales is the flexible* 

The lizard's skin is specific due to scales that form dense tight rows. Lizard scales vary in form from tubercular to plate-like or even largely overlapping each other in formation. The scales originate from the epidermal superficial layer of the skin and form keratinized wrinkles and may have bony plates underlying them (*osteoderms*). They are very close to each other, and links between them allow them to move in all directions. In lizards, scales can vary in form and be modified into crests, spikes, or horns, depending on the type of lizard and on the body part of the lizard and are often of use in taxonomically differentiating species. On the head and on the ventral part, scales are plate-shaped. Scales are important to prevent water loss from the body, as well as to protect the body from injury, because the lizards touch the ground with the ventral surface of the body and thus damage the skin. The skin in the lizard does not follow the growth of the body, so they have to change it, which

In some lizards, it is characteristic that their fingers are covered with large scales. These scales serve them to move easier as in the case of the basilisk lizard (*Basiliscus* 

does not happen in one piece but in several smaller pieces [14].

**138**

*basiliscus*), especially on the water surface or are helpful in the sand skink (*Neoseps reynoldsi*) to move in the sand. Geckos (Gekkonidae) have flattened fingers, characterized by around 20 leaf-like formations on the ventral side of the toes, named lamellas, with a structure that enables animals to climb on the vertical and very smooth surfaces (**Figure 2**). Lamellas consist of seatae (110 μm in length and 4.2μm in width), which are similarly oriented and uniformly distributed in arrays [14]. Each seta branches to form a nanoarray of hundreds of spatular structures, which are 0.2 μm in length and width at the tip which then make adjacent contact with the surface. Gecko setae are formed primarily of β-keratin with some α-keratin components [15].

The skin glands are mostly restricted to certain parts of the body. Thus, in the medial side of the thighs of many lizards, for example, Green Iguana (*Iguana iguana*), there are femoral pores, beneath which femoral glands are located. These glands are larger and usually more developed in males. They secrete a waxed secretion that contains various pheromones relevant to the mating period or when the animal feels endangered. They also help to determine sex in these species [14].

The lizards do not have an external ear; however, in some species, they have a fold of the skin and tympanic membrane that can be seen from the side on the head in a shallow recess. This membrane is covered by a thin membrane in some species that is also changed in the process of ecdysis.

Some lizards such as Green Iguana (*Iguana iguana*) have partial third eye. This organ is a superficial parietal gland which also contains a lens, cornea, and retina, and is located immediately below the skin in the parietal opening between the parietal and frontal bones. The partial eye is a cavitary organ, which is constructed from epithelial cells that contain secretion glands and photoreceptors that convert light stimuli into neuroendocrine messages that can play an important role in thermoregulation but also in hormone production [16].

Lizard skin contains classical skin layers, which can vary in morphology at different positions. Here, we compare skin of the Leopard Gecko (*Eublepharis macularius*) (**Figure 3**) with the skin of the Green Iguana (*Iguana iguana*) (**Figure 4**), both sampled from the dorsal region. The most visible difference in the epidermis was seen in the level of keratinization, where the skin of the Green Iguana was keratinized to a higher extent and the outermost β-layer was much more pronounced. The second most prominent feature observed are the melanocytes, where in the Green Iguana the melanocytes are hardly seen at all. On the other hand, Leopard Geckos can vary very much in color and they exist in various color mutations

#### **Figure 2 .**

*The ventral view of a New Caledonian Giant Gecko (Rhacodactylus leachianus) climbing a vertical glass surface. On the ventral view of the foot of a New Caledonian Giant Gecko, a foot adhesive system is observed with adhesive lamellas which consist of microscale array of setae, which are together clustered in tetrads (Photography, Valentina Kubale).*

#### **Figure 3.**

*Dorsum skin histology of the Leopard Gecko (Eublepharis macularius) by H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, the most visible part is the basal layer with keratinocytes with nuclei, which are dividing by mitosis. In the figure is the part with overlapping scale. The cornified α-layer is very well visible. The intervening mature stratum (mesos) consists of a few layers of cells, which are often not very well seen under this magnification. Partially is also separated from the lower strata as well as the outermost β-layer. In the dermis, fibrous connective tissue, vessels, nerves, melanophores, and Merkel mechanoreceptor cells are observed. (A) 100× magnification, (B) 400× magnification.*

#### **Figure 4 .**

*Dorsum skin histology of the Green Iguana (Iguana iguana) by H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, different layers are observed. The stratum granulosum is not very clearly distinguishable with the nuclei. Cornified α-layer and the outermost β-layer are very visible. In the dermis, fibrous connective tissue, vessels, and nerves are observed. Fibers of the connective tissue are laid in a kind of pattern (A) 100× magnification, (B) 200× magnification.*

(termed morphs). Our sample originates from the most common one, which is basic yellow in color with black spots, which also contains more melanophores. Other morphs include the high yellow (less black spots), hypomelanistic with ten or less dark spots on the body or on the other hand hypermelanistic, which has darker pigmentation but is not black in color. Blizzards are morphs that are completely pattern less. The lavender Gecko has light violet or lavender color included, the tangerine one has an orange color included in its coloration, the carrot tail has orange color on the tail and there are some more variations in color also present in different geckos [14].

#### *3.1.2 The production of color*

Especially important for camouflage (mimicry) is the skin color. Skin color is susceptible to changes depending on the amount of sunlight and it may be darker or lighter. Chromatophores are pigment-containing cells found in the dermis of the

**141**

**Figure 5.**

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

erythrophores, guanophores, and melanophores (**Figure 7**).

*Different color of the skin in the New Caledonian Giant Gecko caused by environment (Rhacodactylus* 

*leachianus) in the same species (Photography, Pia Cigler).*

skin and provide a large range of colors by changing the position of their granules. This ability is particularly significant for the chameleons, although it is also observed to a lesser extent in other types of lizards, such as the New Caledonian Giant Gecko (**Figure 5**), and in some species when light and temperature influence change of skin color to more pronounced such as in the Saharan Uromastyx (*Uromastyx geyri*) (**Figure 6**). The color of the lizard's skin can also be affected by the environment and by the endocrine system [17, 18]. These pigment cells are not just confined to skin but can also occur in the peritoneum of some species, for example in turtles. Animals of the same species during breeding may, due to different mutations, change their basic color and thus produce offspring with new patterns, which are new morphs. Chameleons are an extreme example group of lizards, and, of all the reptiles, they have the highest ability in relation to changing their skin coloration and pattern through combinations of pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise, and purple [19]. Chameleons change skin color depending on the temperature of the surrounding area, their physical condition, intraspecies signaling and communication. Color change is also important for their camouflage. It signals a chameleon's physiological condition and also shows its intentions toward other chameleons [19]. Chameleons tend to show brighter colors when displaying aggression to other chameleons, and darker colors when they signal they are not fighting [20]. Chameleons transform color by changing the space between the guanine crystals which are present in specialized cells named chromatophores. The color change is based upon the wavelength of light reflected off of the crystals. The skin of the chameleons is as in other reptiles consisting of epidermis, dermis, and hypodermis. The important features chameleons have regarding skin color are located in the dermis. It is within the dermis that the blood vessels, nerves, skin muscles, and special cells named chromatophores are present. The chromatophores contain guanine crystals and are subdivided into differing types including iridophores, xanthophores,

### *Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

*Veterinary Anatomy and Physiology*

**140**

**Figure 4 .**

**Figure 3.**

*400× magnification.*

*3.1.2 The production of color*

(termed morphs). Our sample originates from the most common one, which is basic yellow in color with black spots, which also contains more melanophores. Other morphs include the high yellow (less black spots), hypomelanistic with ten or less dark spots on the body or on the other hand hypermelanistic, which has darker pigmentation but is not black in color. Blizzards are morphs that are completely pattern less. The lavender Gecko has light violet or lavender color included, the tangerine one has an orange color included in its coloration, the carrot tail has orange color on the tail and there are some more variations in color also present in different geckos [14].

*Dorsum skin histology of the Green Iguana (Iguana iguana) by H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, different layers are observed. The stratum granulosum is not very clearly distinguishable with the nuclei. Cornified α-layer and the outermost β-layer are very visible. In the dermis, fibrous connective tissue, vessels, and nerves are observed. Fibers of the connective tissue are laid in a kind of pattern (A) 100× magnification, (B) 200× magnification.*

*Dorsum skin histology of the Leopard Gecko (Eublepharis macularius) by H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, the most visible part is the basal layer with keratinocytes with nuclei, which are dividing by mitosis. In the figure is the part with overlapping scale. The cornified α-layer is very well visible. The intervening mature stratum (mesos) consists of a few layers of cells, which are often not very well seen under this magnification. Partially is also separated from the lower strata as well as the outermost β-layer. In the dermis, fibrous connective tissue, vessels, nerves, melanophores, and Merkel mechanoreceptor cells are observed. (A) 100× magnification, (B)* 

Especially important for camouflage (mimicry) is the skin color. Skin color is susceptible to changes depending on the amount of sunlight and it may be darker or lighter. Chromatophores are pigment-containing cells found in the dermis of the skin and provide a large range of colors by changing the position of their granules. This ability is particularly significant for the chameleons, although it is also observed to a lesser extent in other types of lizards, such as the New Caledonian Giant Gecko (**Figure 5**), and in some species when light and temperature influence change of skin color to more pronounced such as in the Saharan Uromastyx (*Uromastyx geyri*) (**Figure 6**). The color of the lizard's skin can also be affected by the environment and by the endocrine system [17, 18]. These pigment cells are not just confined to skin but can also occur in the peritoneum of some species, for example in turtles. Animals of the same species during breeding may, due to different mutations, change their basic color and thus produce offspring with new patterns, which are new morphs.

Chameleons are an extreme example group of lizards, and, of all the reptiles, they have the highest ability in relation to changing their skin coloration and pattern through combinations of pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise, and purple [19]. Chameleons change skin color depending on the temperature of the surrounding area, their physical condition, intraspecies signaling and communication. Color change is also important for their camouflage. It signals a chameleon's physiological condition and also shows its intentions toward other chameleons [19]. Chameleons tend to show brighter colors when displaying aggression to other chameleons, and darker colors when they signal they are not fighting [20].

Chameleons transform color by changing the space between the guanine crystals which are present in specialized cells named chromatophores. The color change is based upon the wavelength of light reflected off of the crystals. The skin of the chameleons is as in other reptiles consisting of epidermis, dermis, and hypodermis. The important features chameleons have regarding skin color are located in the dermis. It is within the dermis that the blood vessels, nerves, skin muscles, and special cells named chromatophores are present. The chromatophores contain guanine crystals and are subdivided into differing types including iridophores, xanthophores, erythrophores, guanophores, and melanophores (**Figure 7**).

#### **Figure 5.**

*Different color of the skin in the New Caledonian Giant Gecko caused by environment (Rhacodactylus leachianus) in the same species (Photography, Pia Cigler).*

#### **Figure 6 .**

*Different color of the skin in the Saharan Uromastyx (Uromastyx geyri) influenced by temperature and sunlight (Photography, Pia Cigler).*

#### **Figure 7.**

*Chromatophores in reptiles (Chameleons) (adapted from Krey and Farayalah [21] and designed by Pia Cigler). Different chromatophores lie in the different layers of the epidermis and dermis. A. Keratin layer, B. Xanthophores, C. Erythrophores, D. Guanophores, E. Melanophores. The three figures show how coloration is achieved through their extensions.*

The iridophores (granulophores) lie in the dermis. They are the most important for true color change, not just changing shades of the same color. They contain semicrystalline nanocrystals of the amino acid guanine (the breakdown of uric acid) that reflects light. They are arranged in a network in a surface and in a deeper layer. In the deeper layer, iridophore crystals have a protective role for the organism against harmful rays. At the surface of the iridophore, smaller crystals are located, which can diffract different wavelengths of light, depending on their arrangement and density. The blue wavelengths are reflected more to produce a blue coloration in an effect called Tyndall scattering. When combined with the yellow carotenoids, they emit green color, which is a common camouflage in many reptiles [9]. Guanophores contain a colorless crystalline substance called guanin and reflect among others the

**143**

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

**4. Snake's skin and scale features**

count the vertebrae without dissection [14].

through the evolution process [22].

blue part of light. Xanthophores produce the pigments called pteridines and are important for yellow shades of the skin. Erythrophores contain the pigment carotene, which they get from the other parts of the body and are important for shades of red. Both types of cells are located above the iridophores and when they cover each other they can form different color combinations. Green color is the consequence of the yellow pigment which covers the refracted blue color coming from iridophores. Melanophores produce the pigment melanin and they lie the deepest within the dermis. Pigment melanin-containing cells give rise to black, brown, yellow, and gray coloration. Albinism in reptiles is caused by lack of melanin. The carotenoid cells are found beneath the epidermis above the melanophores and produce yellow, red, and

orange pigments [9], so albino reptiles are often yellow to orange color.

wavelengths such as yellow, orange, green, and red are reflected [14, 20].

Dispersion of the pigment-containing organelles is only a partial mechanism [17]. Different chromatophores are arranged in two superimposed layers within their skin that control their color and thermoregulation. The top layer contains a lattice of guanine nanocrystals, and by exciting this lattice, the spacing between the nanocrystals can be manipulated, which in turn affects which wavelengths of light are reflected and which are absorbed. Exciting the lattice increases the distance between the nanocrystals, and the skin reflects longer wavelengths of light. Thus, in a relaxed state, the crystals reflect blue and green, but in an excited state, the longer

In snakes, the skin is entirely covered with scales, specific to reptiles. The scales are set together as piles covering each other and are comprised of the upper part of mucosal layer of the skin with subcutaneous tissue below; they are keratinized and protect snakes from skin injuries and dehydration, basically to make it air-proof. When considering the position on the body, they have a different layout and shape. Scales, especially on the head, have an important role in determining the species of snakes. Smaller scales are found dorsally on the body and are placed in several rows. On the ventral, abdominal part of the body, scales are wide and transversally positioned. The shape and number of scales on the head, back, and belly are characteristic to each family, genus, and species. Scales have a nomenclature analogous to the position on the body. In "advanced" (Caenophidian) snakes, the broad belly scales and rows of dorsal scales correspond to the vertebrae, allowing scientists to

Scales protect the body of the snake, aid it in locomotion, allow moisture to be retained within and give simple or complex coloration patterns which help in camouflage and antipredator display. In some snakes, scales have been modified over time to serve other functions such as those of "'eyelash" fringes, and the most distinctive modification—the *rattle* of the North American rattlesnakes. The snakes also use scales for different types of movement because they have lost their limbs

With the abdominal part of their scales, snakes can resist the unevenness of the surface and move across bare terrain such as sand and roads, where they cannot push off rocks and branches (lateral undulation type of movement) and with their muscle strength push their body forward. Besides that, it is mathematically proven

The resistance of a snake's belly scales is highest when its body is sliding sideways, rather than forward or backward. Snakes also seem to lift the parts of their bodies where friction is slowing movement the most, enabling them to slither faster. Snakes can move by folding themselves into pleats, contracting their bellies,

that snakes also rely on the frictional properties of their scales to slide [23].

#### *Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

*Veterinary Anatomy and Physiology*

**142**

**Figure 7.**

**Figure 6 .**

*is achieved through their extensions.*

*sunlight (Photography, Pia Cigler).*

The iridophores (granulophores) lie in the dermis. They are the most important for true color change, not just changing shades of the same color. They contain semicrystalline nanocrystals of the amino acid guanine (the breakdown of uric acid) that reflects light. They are arranged in a network in a surface and in a deeper layer. In the deeper layer, iridophore crystals have a protective role for the organism against harmful rays. At the surface of the iridophore, smaller crystals are located, which can diffract different wavelengths of light, depending on their arrangement and density. The blue wavelengths are reflected more to produce a blue coloration in an effect called Tyndall scattering. When combined with the yellow carotenoids, they emit green color, which is a common camouflage in many reptiles [9]. Guanophores contain a colorless crystalline substance called guanin and reflect among others the

*Chromatophores in reptiles (Chameleons) (adapted from Krey and Farayalah [21] and designed by Pia Cigler). Different chromatophores lie in the different layers of the epidermis and dermis. A. Keratin layer, B. Xanthophores, C. Erythrophores, D. Guanophores, E. Melanophores. The three figures show how coloration* 

*Different color of the skin in the Saharan Uromastyx (Uromastyx geyri) influenced by temperature and* 

blue part of light. Xanthophores produce the pigments called pteridines and are important for yellow shades of the skin. Erythrophores contain the pigment carotene, which they get from the other parts of the body and are important for shades of red. Both types of cells are located above the iridophores and when they cover each other they can form different color combinations. Green color is the consequence of the yellow pigment which covers the refracted blue color coming from iridophores. Melanophores produce the pigment melanin and they lie the deepest within the dermis. Pigment melanin-containing cells give rise to black, brown, yellow, and gray coloration. Albinism in reptiles is caused by lack of melanin. The carotenoid cells are found beneath the epidermis above the melanophores and produce yellow, red, and orange pigments [9], so albino reptiles are often yellow to orange color.

Dispersion of the pigment-containing organelles is only a partial mechanism [17]. Different chromatophores are arranged in two superimposed layers within their skin that control their color and thermoregulation. The top layer contains a lattice of guanine nanocrystals, and by exciting this lattice, the spacing between the nanocrystals can be manipulated, which in turn affects which wavelengths of light are reflected and which are absorbed. Exciting the lattice increases the distance between the nanocrystals, and the skin reflects longer wavelengths of light. Thus, in a relaxed state, the crystals reflect blue and green, but in an excited state, the longer wavelengths such as yellow, orange, green, and red are reflected [14, 20].
