NERVOUS SYSTEM 69 



d. The testes. Remove a testis ; stain, dehydrate and 



clear it, and tease it in balsam mount another 

 in ivater. Examine with a high power. 



The spermatospores are cells, each of which 

 by division gives rise to a large number of sper- 

 matozoa. Only the earliest stages of the division 

 occur in the testes, the spermatospores leaving 

 them as ovoid masses with numerous nuclei, 

 and tuberculated surfaces. 



e. The contents of the vesiculse seminales. Tease in 



water some of the white mass filling the vesicula. 

 Stain another portion, and mount it in glycerine. 



The vesiculas contain spermatozoa in all stages 

 of development : (1) the morula-like spermato- 

 spore as it leaves the testis ; (2) a stage in which 

 the tubercles, or spermatoblasts, are more distinct 

 and are produced outwards into filaments ; (8) 

 later stages in which the filaments are elongated 

 to form the tails of the spermatozoa, while the 

 bodies of the spermatoblasts become their rod- 

 like heads. 



A part of the spermatospore remains un- 

 changed in the centre of the mass, while the 

 peripheral part becomes converted, as described 

 above, into a wisp-like tuft of spermatozoa. 



F. The Nervous System. 



This consists, as in the leech, of a double ventral cord, 

 swollen slightly in each segment ; and a pair of dorsal 

 ganglia in front, connected with the ventral chain by a pair 

 of connectives running round the sides of the alimentary 

 canal. 



1. The nerve-collar is a small ring of nervous substance 

 surrounding the buccal sac just in front of the 

 pharynx, in the third segment. It consists of a pair 

 of pyriform supra-cesbphageal ganglia, united in the 

 median plane ; a pair of lateral connectives running 

 round the sides of the buccal cavity ; and a pair of 



