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 
s+foath 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, which 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 ecdysis in the early autumn; and at this 
time, which is the breeding season, the males seek 
the females with great avidity, 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 which the contained sperma- 
tozoa reach and enter the ova is unknown. The analogy 
