PISCES 



^SS 



in which float red corpuscles and white corpuscles. In the Cyclo- 

 stomata (Petromyzon) the red corpuscles are circular, but in the 

 true fishes they are usually biconvex, flat, oval, nucleated and with 

 hemoglobin, and rich in iron. In the Dipnoi (lung fishes) the red 



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Fig. 1385. Types of tails of fishes. J, diphycercal fin of Polyptertis bichir. 

 (Vertebral column and notochord divide the tail into symmetrical dorsal and ventral 

 portions.) 5, heterocercal tail of the sturgeon. (As a result of an upward bending 

 of the notochord and vertebral column the fin has become asymmetrical, the ventral 

 portion much larger than the dorsal.) C, D, homocercal fins, C, of Amia caka; D, of 

 Trutta salar. (By a still greater upward bending of the notochord and vertebral 

 column the dorsal portion has almost entirely disappeared and the ventral portion 

 almost alone forms the fin, externally apparently symmetrical, but in its internal 

 structure very asymmetrical.) ch, chorda; a, b, c, cover-plates. (From Hertwig- 

 Kingsley. Courtesy of Henry Holt & Co.) 



corpuscles are larger than in most animals (40 mu-mu in diameter) 

 being exceeded in size only by the Urodele Amphibians. Leucocytes 

 are not plentiful in most fishes, but are more numerous in the 

 Dipnoi than in other vertebrates. 



Digestive System. — In the large intestine of the Elasj72obra7ichti 

 there is a spiral valve, lacking in the Teleosteii. The small intestine 



