ix GENITAL ORGANS 313 



The Miillerian duct or oviduct, a wide and conspicuous tube 

 130, B, M.d) in correlation with the large size of the eggs, runs back 

 along the roof of the peritoneal cavity from its funnel, situated on the 

 edge of a suspensory membrane (" falciform ligament ") lying in front of 

 the liver, to the hind end of the cavity where it unites with its fellow of 

 the opposite side before opening into the cloaca (Fig. 130, B, cl). A 

 peculiarity of the Dogfish and some of its allies is that the funnels of the 

 two oviducts are merged together into a single opening. A portion of 

 the duct near its anterior end is swollen up to form a somewhat ellipsoidal 

 body the oviducal gland (Fig. 130, B, od). The secretion of this is 

 deposited round the egg during its passage, so as to enclose it, together 

 with a small quantity of albumen or white, in a shell of horny consistency 

 and of a characteristic pillow-case shape, with the four corners drawn out 

 into elastic tendrils which at the time the egg is laid are coiled round 

 seaweeds so as to anchor it in position. 



In the male Miillerian ducts make their appearance just as in the 

 female, but in this case they gradually atrophy so that in the adult all 

 that remains is the peritoneal opening, leading into a tapering pocket 

 upon each side representing the anterior end of the duct (Fig. 130, A, M.d). 



The Wolffian duct is in the female a simple straight tube which runs 

 back along the ventral side of the opisthonephros, becoming considerably 

 dilated posteriorly and uniting with its fellow before opening into the 

 cloaca at the tip of a small papilla situated immediately behind the 

 opening of the oviducts. In the male the arrangement becomes much 

 more complicated. The fused posterior portion of the ducts the urino- 

 genital sinus (Fig. 130, A, u.g.s) is much larger and it bulges forwards 

 on each side as a pointed projection known as the sperm-sac (s.s). The 

 main portion of the duct, lying in front of this, pursues an extremely 

 sinuous course along the ventral face of the anterior half of the opistho- 

 nephros, receiving as it does so the collecting tubes or terminal portions 

 of the tubules of this part of the kidney. Posteriorly it becomes straight 

 and at the same time much dilated forming the seminal vesicle (s.v). 

 The collecting tubes of the posterior, functionally renal, part of the 

 opisthonephros no longer open directly into the Wolffian duct but lead 

 into a separate urinary duct (" ureter " Fig. 130, A, u) which opens 

 independently into the posterior fused portion of the ducts (urino-genital 

 sinus). 



Finally it must be noticed that in the male a portion of the pelvic 

 fin on its inner side is modified to form a clasper which functions in 

 the conveyance of the microgametes into the cloaca and oviduct of 

 the female. The microgametes make their way by active swimming 



