KEPEODUCTIVE SYSTEM 47 



like end. These anterior nephridia are smaller 

 than the succeeding ones. 



b. From the eighth to the sixteenth somites, i.e. those 



in which the testes are situated, the nephridia 

 have the characters detailed above. 



c. The two hindmost pairs of nephridia, in the seven- 



teenth and eighteenth somites respectively, have 

 well-developed testis-lobes, with cauliflower heads 

 lying in peri-nephrostomial sinuses. 



D. The Reproductive System. 



The leech is hermaphrodite, but does not impregnate its 

 own ova. 



1. The male organs. 



a. The testes are nine pairs of spherical sacs lying 



in the somites from the eighth to the sixteenth 

 inclusive. They are placed in the ventral region 

 of the body at the sides of the ventral sinus. 

 Each pair lies mainly in the second, but partly in 

 the first annulus of the somite in which it occurs. 

 The segmental repetition of the testes is note- 

 worthy. Sometimes a tenth or even an eleventh 

 pair of testes may be present. 

 i. The spermatozoa. 



Bemove one of the testes, and tease it on a slide in salt 

 solution. Cover, and examine with low and high powers. 



Spermatozoa in various stages of develop- 

 ment will be seen. 



b. The vasa efferentia are a series of short sinuous 



ducts which run outwards from the testes, and 

 open into the vasa deferentia. 



c. The vasa deferentia are a pair of longitudinal tubes 



which run forwards in a sinuous course along 

 the ventral body- wall, about midway between the 

 testes and the vesicles of the nephridia. 



In front of the first pair of testes they continue 

 their course through the seventh somite, and in 

 the sixth enter the vesiculae seminales. 



