t 



middle of body cavity 



i 



nterrenal gland 



bladder 



urinary sinus 

 urinary pore 



epididymis 



vas deferens 

 posterior end of Leydig's gland 



urogenital gland 



urogenital pore 



Mullerion duct 

 ampulla 



nterrenal gland 



openings of ureters 



A B C 



Figure 10-49. Urogenital systems of the chimaerid, Hydro/ogus. A, kidneys of adult female (see 

 Figure 9-25 for relationships to reproductive tract and viscera in general); B, ventral view of mole 

 systems, showing testes lying in anterior port of body cavity; C, laterol view of male systems. 



single band (25 to 30-mm larva). The stroma surrounding 

 the gonocytes, or germ cells, appears to be of epithelial ori- 

 gin but could include cells from the mesenchyme of the kid- 

 ney anlage. The gonadal ridge extends through the posterior 

 two-thirds of the body cavity, reaching almost to the poste- 

 rior end. According to Lubosch (1903), about 25 per cent of 

 the larvae have hermaphroditic gonads but later become 

 males by loss of the ovocytes. Of adults, appro.ximately half 

 are of either sex. In the male the clumps of germ cells form 

 follicles, which when ripe rupture into the body cavity. In 

 the female the germ cells become surrounded by follicle 

 cells of the stroma which contribute to the development 

 of the egg. The eggs rupture into the body cavity at 

 maturity. 



The sex cells leave the body by way of the abdominal 

 pores. These bilateral apertures in the wall of the urogenital 



sinus are similar in the two sexes. They open a few weeks 

 before spawning. Injection of oestrone or anterior pituitary 

 will cause perforation of these pores in the young lamprey. 



Myxinid The single gonad appears late as a structure at- 

 tached to the gut just to the right of the mesentery. The an- 

 terior part develops first and produces ovocytes; the poste- 

 terior part develops first and produces ovocytes; the poste- 

 rior part produces spermatocytes. In fish less than 20 cm 

 long, none can be identified as males, but by 24 cm the two 

 sexes are defined. However, both have a rudimentary area 

 In the adult the gonad stretches nearly the entire length 

 of the body cavity. Its supporting mesentery is attached to 

 the gut wall to the right of the mesentery. The testis is 

 folded and lappeted; the sperm-producing follicles are nu- 

 merous, the mature follicles at the surface, the younger fol- 



336 • THE UROGENITAL SYSTEM 



