ductus epididymidis 

 marginal canal 

 ductuli efferentia 

 sequence of ripening testicular ampullae ^ L/^^\ 



ductuli efFerentia 



■M 

 R 



-Leydig's gland 



- excretory part of kidney 



_vas deferens 

 (nephric duct 



"ureter" 



nephric duct 



Mtjilerian duct. 

 -Seminal vesicle 



opening of gut into cloaco 



MALE 



urinary papilla 



FEMALE 



Figure 10-48. Urogenital systems of the shark. A, mole Squo/us; B, 

 relationship of testicular ampullae and tubules in Scyllium con/cu/a; C, 

 urinary system of female Scyllium; D, urogenital ducts and cloaca of 

 female Squalus. (A and D after Marinelli and Strenger, 1959; B and 

 C after van den Broek, 1933} 



ampullae to the urogenital sinus where they end blindly 

 above the urogenital gland. In the very young the urogenital 

 gland is small; it is larger in the adult although it may be 

 embedded in connective tissue and not apparent. The male 

 has anterior and posterior pelvic claspers utilized in copula- 

 tion (Figure 10-49). 



The female (Figure 9-25) is similar to the shark in the 

 position of the ovary, the general nature of the oviduct, and 

 the large, shelled eggs. The Miillerian ducts have a common 

 midline ostium, below the esophagus, and each has an ex- 

 panded nidamental gland area. Also there are regions identi- 

 fied as the isthmus, uterus, and vagina. The oviducts open 

 individually, lateral to the excretory pore in a shallow uro- 

 genital sinus. Anterior to the excretory pore and behind the 

 anal opening is an opening into a blind-ended sac which 

 has been called the seminal receptacle. 



The young female is presumed to have a more marked 

 urogenital sinus. The anterior wall of this sinus forms a 

 forward-extending bladder or sac, the seminal receptacle. 

 In the mature female, with the partial aversion of the uro- 

 genital cavity, the sac comes to open anteriorly, while the 

 Mijilerian ducts open lateral to the excretory pore (Figure 

 10-49). The small urogenital gland of the male may be the 

 homolog of the seminal receptacle of the female. 



General observations Only the middle part of the genital 

 ridge develops in sharks. The genital fold hangs down into 

 the body cavity with no tendency for its margin to roll 

 laterally (Figure 10-50). The germ cells lie on the lateral 

 surface of the fold. The same relationships of cortex in the 

 female and medulla in the male, as observed in amphibia 

 and higher forms, appear to hold. 



Heplanchus is described as having a rudimentary testis in 

 females; the testis lies above the ovary along the line of at- 

 tachment of the mesovarium. In a number of immature 

 males of this shark, rudimentary ovaries were observed ly- 

 ing below the testis and fused at the ventral midline. The 

 Miillerian ducts of these males had a single midline funnel 

 but reached only part way posteriorly. The relationship of 

 male organ to the attachment area of the gonad and the fe- 

 male organ to the more ventral cortical part of the ridge 

 agrees with observations in the higher forms. 



The origin of the Miillerian ducts from the pronephric 

 funnels and the splitting of the nephric duct appears to be 

 distinctive for this group. The fairly close agreement in this 

 area of anatomy between the holocephalan and sharks, which 

 in other respects seem to be so diverse, suggests that they 

 are indeed derived from a common anestor, an ancestor 

 having Miillerian ducts in the female and a Leydig's gland 

 as well as an epididymis in the male. 



Cyclostomes 



Lamprey The gonad of the lamprey is an irregularly lo- 

 bate mass suspended by a midline mesentery (Figure 10-26), 

 and, in the ripe condition, it may even fold around the in- 

 testine. The gonad, whether testis or ovary, extends almost 

 the entire length of the body cavity. There are no reproduc- 

 tive ducts. 



The germ cells appear in the early larva on either side of 

 the body and migrate to the midline where they form a 



THE REPRODUCTIVE SYSTEM 



335 



