GERM CELLS OF ARGAS 649 



smaller granules fuse together to form large irregular masses. 

 At no time in their history do the mitochondria take their char- 

 acteristic stains more readily than now, and in the living cell 

 this ring is a most striking object. Figure 15 also shows the 

 manner in which the vesicular bodies approach the nucleus, al- 

 though, as a matter of fact, they should scarcely be spoken of 

 as vesicles at this time since they are apparently breaking up. 

 Lying mostly between these structures and the mitochondrial 

 ring are now seen certain other substances (o.d.) which appear 

 as homogeneous globules in the living cytoplasm and which, 

 as will later appear, are to be considered as oil droplets. 



Between the stage represented by figure 15 and that in figure 

 19 striking changes occur in the general form of the cell, leading 

 toward the formation of the spermatozoon. The vesicular bodies 

 entirely disappear and the oil droplets increase in number. 

 Little change occurs in the constitution of the mitochondrial 

 ring except a further condensation of its component granules and 

 the migration of the ring as a whole toward the nuclear pole of 

 the cell. The external form of the cell, however, is modified by 

 the invagination of that region which lies immediately opposite 

 the nuclear pole (i.e.), while at the same time the striated layer 

 becomes transformed into a mass of cilia-like threads (c.p.) 

 which project into the invagination cavity. These threads 

 remain short in the region formerly marked by the cap of shorter 

 striations while in the former equatorial region the threads are 

 longer than the original striations (fig. 18). The oil droplets 

 show no change. 



From this period until the outer tube of the spermatozoon 

 develops the changes which occur are shown in figures 19, 20, 21, 

 22, and 23. The mitochondrial ring loses its distinct form and 

 the large granules of which it is composed break up to form 

 smaller granules (figs. 22 and 23). The nucleus moves to one 

 side of the cap of cytoplasm. The cell wall immediately beneath 

 the shorter cilia-like threads thickens and these threads elongate 

 to form a little tuft which projects downward into the invagina- 

 tion cavity (figs. 22 and 23). The opening into the cavity 

 becomes progressively smaller. 



