THE PROCESS OF FERTILIZATION. 135 



of the finest branches of the ducts of the testis. The 

 cavity of each vesicle is filled by the large nucleated cells 

 which line its walls (fig. 33, B), and, as the breeding 

 season approaches, these cells multiply by division. 

 Finally, they undergo some very singular changes of 

 form and internal structure (fig. 34, A — D), each becom- 

 ing converted into a flattened spheroidal body, about 

 T-yo^th of an inch in diameter, provided with a number 

 of slender curved rays, which stand out from its sides 

 (fig. 34, E — G). These are the spermatozoa. 



The spermatozoa accumulate in the testicular vesicles, 

 and give rise to a milky-looking substance, w^hich traverses 

 the smaller ducts, and eventually fills the vasa deferentia. 

 This substance, however, consists, in addition to the 

 spermatozoa, of a viscid material, secreted by the walls 

 of the vasa deferentia, which envelopes the spermatozoa, 

 and gives the secretion of the testis the form and the 

 consistency of threads of vermicelli. 



The ripening and detachment of both the ova and 

 the spermatozoa take place immediately after the com- 

 pletion of ecdj'sis in the early autumn ; and at this 

 time, w^hich is the breeding season, the males seek 

 the females with great aviditj^, in order to deposit the 

 fertilizing matter contained in the vasa deferentia on the 

 sterna of their hinder thoracic and anterior abdominal 

 somites. There it adheres as a whitish, chalky-looking 

 mass ; but the manner in wdiich the contained sperma- 

 tozoa reach and enter the ova is unknown. The analogy 



