TEGUMENTARY SYSTEM. 131 



The transition from the Naked to the Squamigerous Reptiles 

 appears to be effected by those kinds of Reptiles, as the Chameleon, 

 that are provided with a thin and delicate epidermis, having be- 

 neath it soft tubercles or excrescences, endowed with the power to 

 expand and contract. These tubercles, which are continued also 

 upon the circular eyelids, are separated from each other by strong 

 annular layers of fibres, and consist of a bed of fibro-cellular tissue, 

 within which a double layer of pigmentary cells may be detected. 

 The most superficial pigmentary cells are black, either small and 

 rounded, or of larger size and ramified, and beneath them are found 

 some smaller nucleated cells or spots of a bright red color. The 

 general appearance of these structures remind us very strikingly 

 of the chromatophorous cells of the Cephalopoda, and it is probable 

 that in the living Chameleon the same lively contraction of the 

 walls of the cells may take place as in the Cuttle-fish ; and to this 

 property may be owing the well-known power of changing color which 

 that animal possesses. In specimens preserved in spirits of wine, 

 these cells may be rendered beautifully distinct by treating the skin 

 with caustic potash. 



The Squamigerous Reptiles exhibit various degrees in the devel- 

 opment of their epidermic structures, giving rise to those numerous 

 diversities of form which it is the special province of Zoology to 

 depict. Frequently, as in the Snakes, in Scincus and other Sau- 

 rians, scales are found that overlap each other like tiles, as in 

 Fishes, or are disposed in a quincunctial order, or so as to form 

 annular bands, as in Ophisaurus. Scutes, provided with tubercles 

 and spines, are also commonly met with, or large plates containing 

 bony matter, as in the Crocodiles and Chelonia ; in the latter indeed 

 they constitute true dermal bones, which coalesce with the skeleton, 

 and form the dorsal and ventral shields, as will be described more 

 minutely further on. The laminae or scuta of the epidermis are 

 formed by the coalescence of horny cells, which may be brought 

 into view by submitting the scales of a tortoise to the action of 

 caustic potash. 



The scales of the Snakes exhibit under the miscroscope very deli- 

 cate longitudinal and transverse striae, which are probably caused 

 by the coalescence of cells. In the parts of the epidermis situated 

 between the scales, the cellular structure may be often more dis- 

 tinctly recognised. The epidermis is cast several times during the 

 year, either piecemeal, or like the exuvia of the caterpillar, in one 

 entire piece from off the whole surface of the body. A kind of 



