CHAPTER VI 



REPTILIA 



The reptiles are represented today by the turtles, alligators, 

 lizards, snakes, and a small group of New Zealand reptiles. These 

 are divided into five orders. The numerous fossil orders and the 

 recent reptiles form four distinct sub-classes. Three of these are 

 represented today. Most of the reptiles disappeared after the 

 mammals arose and the reptiles ceased to rule the land areas of 

 the earth. Reptiles can be identified in the field by their ecto- 

 dermal scales which give the animal a rough feeling when the 

 hand is drawn from the tail toward the head. There is no truth 

 in the belief that snakes and lizards are slimy, their skins being 

 remarkable for the lack of integumentary glands. 



Anatomically the living reptiles vary widely from each other, 

 and from other living groups. The great gulf which separates 

 amphibia from reptiles is based upon their embryology. All 

 reptiles lay large yolked eggs (which may be retained in the 

 oviducts until time of hatching from the egg membranes) and 

 the young begins life as a small adult. There is never a larval 

 period; and though the reptiles, like all other vertebrates, have 

 gill slits during the embryonic period, there is never a sign of 

 gills. Embryonic respiration takes place through the shell, and 

 the blood is oxygenated through a specialized breathing structure, 

 the allantois, which is an outpocketing of the posterior end of the 

 primitive gut and disappears at the time of hatching. Reptiles 

 also develop an amnion, an enveloping, fluid-filled, protective 

 embryonic membrane. This is in correlation with their land life, 

 the surrounding fluid acting as a buffer against any chance blow 

 and preventing drying of the embryo. These membranes are also 

 found in the birds and mammals, with the result that all three 

 of the higher classes of vertebrates are included together as the 

 Ajnniotes. 



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