PISCES 



m 



All the Cyprinidae lack peptic glands. Babkin and Bowie ^ have 

 shown that Fundulus heteroclitus has no stomach, that pepsin and 

 HCl are absent and that every phase of digestion takes place in an 

 alkaline medium. 



Fig. 1 40. Scorpaenoid fish. (Courtesy of Amer. Mus. of Nat. Hist.) 



Ljonph. — Fishes have small vessels (the lymph capillaries), 

 lymph spaces, and lymph sinuses. In the eel a lymph heart in the 

 tail communicates with the smaller of the two caudal veins and 

 rhythmically pumps lymph into the vein. Lymph consists of 

 plasma minus red corpuscles, but normally rich in the white corpus- 

 cles with large nuclei called lymphocytes. 



Endocrine Glands. — The thyroid gland in the Elasmobranchs is a 

 large compact organ near the anterior end of the ventral aorta. 

 In the Teleostomi it is sometimes paired or as in the perch consists 

 of diffuse masses of reddish lobules scattered along the afferent 

 branchial artery. The thymus gland of the embryo Elasmobranchs 

 and Teleosts has a multiple origin, arising from a series of epithelial 

 thickenings, one of which is developed at the dorsal extremity of 

 each of the gill clefts except the spiracle. The rudiments invaginate 

 and fuse. The thymus of the adult Elasmobranchs is paired, the 

 organ lying just above the branchial arches. In the Teleostomi, the 

 thymus is found at the dorsal extremity of the last branchial arch 

 near the mucous membrane of the branchial cavity. The pancreas 

 is represented in teleosts by the pyloric appendages, while isolated 



« Babkin, B. P., and Bowie, D. J. 1908. The digestive system and its function 

 in Fundulus heteroclitus. Biol. Bull., vol. 54, no. 3, pp. 254-277. 



