208 



BONY FISHES 



The ultimobranchial gland is a mass of cells developed from the 

 last branchial pouch and perhaps related to the parathyroids. 



The hormone rennin, which raises the blood pressure, is said to be 

 present in freshwater teleosts, with their high glomerular filtration, 

 but not in marine ones. 



The gonads produce steroid hormones as in elasmobranchs (p. 

 167). The secondary sex characters depend upon their presence, thus 



ns. c. 



n.e 



Fig. 127. Comparison of pattern of organization of the caudal neurosecretory 

 system (b) with the hypothalamo-hypophysial system (a). 



ah. adenohypophysis; b.v. blood-vessels; c.c. central canal; /.i. filum terminale; h. 'Herring 

 bodies', neurosecretory products; n. neurohypophysis; n.e. nerve endings; ns.c. neurosecre- 

 tory cells; o.c. optic chiasma; p. pituicytes; p.v. hypophysial portal vessels; r.f. Reissner's fibre; 

 11. urohypophysis; v. vtntricle. (After Enami, N., in Symposium on Comparative Endocrinology. 



Wiley, New York.) 



the gonopodium of the male of viviparous fishes (p. 267) is developed 

 if sex hormone is added to the water. 



At the hind end of the spinal cord of fishes is a small lump consisting 

 of masses of secretion produced by neurosecretory cells of the spinal 

 cord and hence called the urohypophysis (Figs. 126 and 127). In 

 function it appears to be connected with salt regulation; injection of 

 hypertonic NaCl produces hypersecretion, the products accumulating 

 at the cut surface if the cord has been severed. Injection of extracts 

 produces changes in the sodium content of the fish and also changes 



