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CLASSIFICATION OF ANIMALS 



bony, though parts remain cartilaginous in the adult. The 

 skeleton is so much like that of the higher vertebrates that 

 most parts can be accurately homologized. The same is true 

 of the digestive tract. There is a cloaca into which the intes- 

 tine, the ureters and the genital ducts open. On its ventral 

 wall there is a large pocket, the urinary bladder. The lungs are 

 simple sacks with the walls usually more or less folded like a 

 honey comb. The thin skin also acts as a respiratory organ. 



Fig. 172. — Outline drawings of three urodele amphibians showing successive 

 stages in degeneration of the appendages. A, Siren; B, Amphiuma; C, Necturus. 

 (From Galloway, after Mivart.) 



The kidneys open into the cloaca by a pair of ureters. The 

 oviducts are two long convoluted tubes beginning in the anterior 

 part of the body cavity by large funnel-like openings and lead- 

 ing separately into the cloaca. The male gonads are connected 

 with the kidneys and the sperm reaches the cloaca by way of the 

 urinary tubules. The nostrils have an opening into the anterior 

 part of the mouth. The brain is well developed but the cere- 

 bellum is small. 



638. Order i. — The Gymnophiona are worm-like Amphibia, without 

 appendages. The trunk is elongated and the tail rudimentary. The 

 skin is filled with small scales. The chorda is persistent. The eyes are 



