FROM EGG TO INSECT SNODGRASS 



383 



sperm cells are thus differentiated, one having the usual chromo- 

 some formula of 2-|-la?, the other having simply two orthochromo- 

 somes (fig. G, h). At the second maturation division, Avhen all the 

 chromosomes divide in the usual manner, four cells are formed, two 

 of which are of the Ix variety, and two of the no-a? variety (fig. G, c). 

 In cases where a y-chromosome is present with the aj-chromosome, 

 there are still two classes of sperm cells produced, one having the 

 a?-chromosome, and the other the y-chromosome, since these chromo- 

 somes are separated in the first division after their union in synapsis. 



Fig. 7. — Spermiogenesis, or the transformation of the male germ cell after maturation 

 into a spermatozoon, and the mature spermatozoon 

 A-J, spermiogenesis in a grasshopper (figures from H. S. Davis) : a, head of the 

 spermatozoon ; h, the middle piece, from which a long filament extends out into the 

 tail ; c, the tail, formed by elongation of the cell body (B, C, D) ; d, a body in the 

 cell (A, B) that eventually surrounds the tail filament (D, E) ; Nu, the nucleus, 

 which remains in the head (J). K, bundles of spermatozoa from the spermatheea of 

 a female broad-winged katydid. 



The divisions of the male germ cells always affect the entire cell, 

 since the male cells do not accumulate yolk, and remain small. Fur- 

 thermore, the maturation of the male cells, with few exceptions, pro- 

 duces four equal-sized cells, all of which ordinarily will become 

 functional spermatozoa. At this stage each sperm cell, now known 

 as a spermatid^ still has the rounded or oval form of an ordinary cell. 

 To become a fully-formed spermatozoon it must undergo a meta- 

 morphosis, a process too complicated to be described here in detail, 

 but which results in a transformation of the simple spermatid into a 

 thread-like spermatozoon (fig. 7). The mature spermatozoon, how- 



