334 



THE DOGFISH. PHYLUM CHORDATA 



j^l. 



-tyiso. 



r.t.-- 



Li.-l- 



,ves.sem 



- fp. s. 



minute tubules, many of which have a small opening, the peritoneal 



funnel, into the coelom ; the 

 vertebrate kidney is made in fact 

 of a series of coelomoducts, com- 

 parable to those of annelids and 

 arthropods but not homologous 

 with nephridia. At their outer 

 ends the tubules of the anterior 

 part open into a Wolffian duct 

 which runs on the ventral surface 

 of the kidney, and the tubules of 

 the hinder part into five or six 

 urinary ducts. In the female the 

 Wolffian duct is straight, and 

 widens at its hinder end to form 

 a urinary sinus, which joins its 

 fellow to open into the cloaca 

 upon a median urinary papilla ; 

 the urinary ducts open separately 

 into the urinary sinus. The 

 Wolffian duct of the male is coiled, 

 and, as is usual in vertebrates, 

 receives also the products of the 

 testis ; its posterior part is swollen 

 to make a seminal vesicle, which 

 opens into a urogenital sinus. The 

 urinary ducts unite to form a 

 single duct (often miscalled the 

 ureter) which also opens into the 

 urogenital sinus ; this has two 

 blind forward-running diverticula, 

 the sperm sacs, lying on the ventral 

 surfaces of the seminal vesicles, 

 and opens into the cloaca on a 

 urogenital papilla. The sperm sacs 

 represent the oviducts of the 

 female. 



The principal end-product of 



nitrogenous metabolism is urea. Much of this, however, is 



retained in the blood (see p. 333). ^ 



rin. 



u.g.p. 



Fig. 252. — The reproductive organs 



of a male dogfish. The testes are 



displaced to the animal's right, 



and only the left kidney is 



shown. 



c/., Cloaca ; i.o.d., rudiment of internal opening 

 of oviducts; l.t., left testis; k., k'., an- 

 terior and posterior parts of left kidney ; 

 tnso., mesorchium ; oes., oesophagus ; r.t., 

 right testis ; rm., rectum ; s./., suspensory 

 ligament ; sp.s., left sperm sac ; u.g.p., 

 urinogenital papilla ; u.g.s., urinogenital 

 sinus ; ur. ureter ; ur'., ducts of posterior 

 part of kidney ; v.eff., vasa efiferentia ; ves. 

 sent., vesicula seminalis ; W.d., Wolffian 

 duct or vas deferens. 



