TUB LOWER VBRTEBRATA. 



189 



partly confluent at the posterior end. From the anterior 

 ends of these, a series of vasa efferentia run to a body which 

 obviously is the anterior portion of the kidney, as in the 

 frog. But this has its own separate duct the vas deferens, 

 quite distinct from the ureter. This vas deferens is dilated 

 posteriorly into a large cylindrical tube, which is called the 

 seminal vesicle (though obviously not quite the same' thing 

 ns the frog's seminal vesicle), and this opens into a median 

 urogenital sinus, which opens by a single aperture into the 

 cloaca. From the urogenital sinus one or more pairs of 

 blind sacs, the sperm-sacs, come off. 

 Externally the male is distinguished by 

 the daspers ( 13), by which he grasps 

 the female while injecting the seminal 

 fluid into the cloaca and oviducts. 

 Fertilization of the eggs must take 

 place high up in the oviduct, before 

 the egg enters the oviducal gland. 



Fig. 100. EGO-CASE OF 

 DOGFISH. 



19. Excretory System, The kid- 

 neys in the male are a pair of lobulated 

 bodies which extend from a little be- 

 hind the pericardium to beyond the 

 cloaca posteriorly ; but as the anterior 

 part is specially connected with the 

 reproductive system and has a duct of 

 its own, it is advisable to apply separate 

 names to them. We may use the same 

 terms as in the rabbit and call the anterior part epididymis 

 and the posterior part kidney ; or we may use terms that 

 will be explained more conveniently in the chapters on 

 Development, and call the anterior part mesonephros, the 

 posterior, metanephros. In the latter case we call the 

 vas deferens the mesonephric duct and the ureter the 

 metanephric duct. 



In the female the mesonephros is in a vestigial condition 

 and has no separate duct. The metanephros or true kidney 

 is like that of the male. 



In both sexes the metanephric ducts open into a median 

 sinus, and this opens by a median aperture on a small 



