^s 



efferent duct 



-expanded (bladder) 

 nephric duct 



ovary 



_coelomic funnel 



continuous with 

 parovarial ovary 



opening from funnel 

 into nepfiric duct 



MALE 



B FEMALE 



LEPISOSTEUS 



Figure 10-46. Reproductive tracts of mole and female of tepisosteus 

 OS seen in ventral view. (In port after von den Broek, 1938) 



acquires new connections posteriorly, but usually opens by 

 a genital pore. 



The salmon type of sy.stem is the result of reduction of the 

 primitive oviducts. In the young salmon the ovary shows a 

 slight lateral fold ventrally but remains free of the body wall. 

 The genital ridge extends posteriorly first in the swim blad- 

 der, then on the mesentery of the gut. It disappears near the 

 posterior margin of that mesentery but reappears on either 

 side of the terminal part of the gut. Here it extends out and 

 up to fuse with the body wall, thus forming the floor of the 

 posterior, midline funnel serving for exit of the eggs from the 

 body. This funnel breaks through to the exterior between 

 the urinary pore and the anus at spawning time. 



The similarity of sexual ducts in male and female teleosts 

 suggests that they are the same. Actually the male duct is 

 the result of posterior extension of the central canal through 

 the genital ridge, while the female duct is the result of a 

 folding or invagination process, i.e. the oviduct lying above 



the lateral to the primitive ridge. An interesting situation is 

 observed in Lestidium affine, where the hermaphroditic gonad 

 has both male and female ducts, the former dorsomedial to 

 the latter. The male ducts enter the urinarv- sinus separately; 

 the female ducts unite and exit between the excretory pore 

 and anus. 



The genital ridge of the teleost is also peculiar because it 

 contains no obvious mesonephric blastema; it is essentially 

 cortical. There is the possibility of inclusion of some mes- 

 enchymatous cells which arose near or in the mesonephric 

 blastema. These cells appear to form part of the stroma, a 

 tissue mass enclosing germ cells, and as such are not lo- 

 calized as in the gonadal ridge of higher forms, where there 

 is a cortex and a medulla. Some teleosts are hermaphroditic 

 and in these the ovarian part lies anterior to the testicular 

 part. 



Chondrichthyes 

 Shark 



THE MALE The testis is large and suspended by a broad 

 mesorchium (Figure 10-48). The position in the body cavity 

 varies from far anterior back to about the middle. The right 

 is usually larger than the left. 



In Scytlium there is a sequence of developmental stages of 

 seminal ampullae. This sequence starts from the ventral free 

 margin where new follicles are forming and progresses to- 

 ward the dorsal attachment. At the time of breeding, a set 

 of ripe ampullae connects through narrow ductuli recti with 

 the central canal, which lies along the attached margin of the 

 gonad. Many of the ampullae observed along the canal are 

 empty; these are spent ones of previous reproductive periods. 

 The testes of most sharks are made up of typical ampul- 

 lae, each connected with the central canal and each giving 

 rise to repeated generations of germ cells. In some sharks 

 the testis is associated with an epigonal organ which is 

 lymphoid in nature. This extends back to the cloaca in 

 Galius; it may be relatively small as in Heptanchus or absent 

 as in Squalus. Perhaps as an epigonal extension, the testes of 

 Scyllium meet and fuse posteriorly. 



The central canal, which may form a reticulated set of 

 channels, is drained by one or a few anterior efferent ducts. 

 These enter the epididymis. Peritoneal funnels may remain 

 in this part of the kidney but lose connection with the 

 modified nephric tubules. The epididymis is highly devel- 

 oped and associated with the Leydig's gland (see description 

 of shark kidney). 



The nephric duct is distinctly modified for sperm tran- 

 sport and may be separate from one or several ureters 

 carrying the excretory fluid to the cloaca. Its posterior 

 third, approximately, is expanded as a glandular ampulla 

 which has a reticulum of folds on its inner surface. A termi- 

 nal evagination from the nephric duct occurs in some species 

 (Scyllium); this is the vesicula seminalis. In both sexes of 



THE REPRODUCTIVE SYSTEM 



333 



