354 AN INTRODUCTION TO THE STUDY OF FOSSILS 



Order 4, Gymnophiona 



Snake-like, without limbs or tail. Examples are the tropical, 

 subterranean coecilians. Fossil remains are unknown. , 



1. In what ways are the Amphibia an advance upon the 

 fish ? 



2. Name one way in which the embryo shows its fish ancestry. 



3. What is the habitat of the Amphibia ? 



4. Give the significance of the name. 



5. What is the geologic range ? 



6. Name the four orders into which Amphibia are divided, 

 with a living example of each existing order. 



7. Outline the development of a toad. 



8. Give an example of the Stegocephalia. Why are these 

 included with the Amphibia ? 



Class E, Reptilia 



Cold-blooded vertebrates, usually with two pairs of five-toed 

 limbs and a horny exoskeleton of scales {e.g. snake, lizard), 

 or of horny {e.g. tortoise) or bony {e.g. Stegosaurus) plates. 

 Thorax usually near head, hence the short neck. Living reptiles 

 periodically cast off this horny exoskeleton either as a whole 

 or in fragments. They breathe by lungs throughout life. The 

 heart is incompletely four-chambered, the two ventricles being 

 separated by a partial partition. There is no metamorphosis, 

 the young leaving the egg in the adult form ; hence the eggs are 

 large. Reptiles are mostly oviparous. Unlike the Amphibia, 

 the structure of reptiles is such that they could adapt them- 

 selves to dry air, and could hence spread more widely upon 

 land. 



Reptiles were very abundant and dominant during the entire 

 Mesozoic time; they ruled not only the earth and sea but the 

 air as well. 



Derivation of name. — Reptilia > Latin reptilis, creeping ; 

 from the mode of progression of snakes, the best known of 

 reptiles. 



