384 KATHARINE FOOT. 



EXPLANATION OF PLATE II. 



FIG. 19. Numerous heads of spermatids shortly after the second division. 

 They are at first round, as demonstrated in the figure, and, as a rule, elongate 

 before the appearance of the tail. In the elongated heads of this figure the middle- 

 piece (?) is in evidence and from this point the tail develops. 



FIGS. 20 to 27. Successive stages of the development of the spermatid into 

 the mature spermatozodn. In Figs. 20 and 21 the middlepiece is demonstrated, 

 the tail developing from this point. In Figs. 22 and 24 both the middlepiece and 

 the acrosome (?) are demonstrated, the spine developing from the latter. Fig. 25 

 shows an early stage of the development of the spine. Figs. 26 and 27 demonstrate 

 the mature spermatozoon in which the head and spine are fully developed. At this 

 stage the middlepiece and acrosome are obscure. 



