48 THE LEECH 



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

 in which the testes are situated, the nephridia 

 have the characters detailed above. 



e. 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. 



Leeches are hermaphrodite, but do not impregnate their 

 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 situated 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 and even an eleventh 

 pair of testes may be present. 



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 development 

 will be seen. 



b. The vasa eflferentia are a series of short sinuous 



ducts which run outwards from the testes, and 

 open into the vasa deferentia. 

 0, 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 vesiculse seminales. 



