GERM CELLS OF ARGAS 657 



sive alteration, becoming pear-shaped in form and later more 

 elongated. The chromatin, which heretofore has been diffuse, 

 aggregates into threads which stain intensely with nuclear dyes. 

 The nucleus now orients itself in relation to the finger-like 

 process in such a manner that the more pointed end projects 

 into the basal portion of this process. 



During the course of its formation the outer tube is bent upon 

 itself and coiled around its basal region although the arrange- 

 ment of the loops is not always similar to that shown in figure 

 27. At this stage the developing spermatozoa are packed closely 

 together, and only in teased preparations and in smears can 

 their individuality be distinguished. As the tube grows out- 

 ward it is surrounded by a gelatinous envelop (g.e.) which in- 

 creases in amount as the tube develops and apparently serves 

 to hold the coils of the tube together. This enveloping gelati- 

 nous mass persists until the spermatozoa are near the completion 

 of their metamorphosis. 



Figures 27 and 28 picture the genesis of a structure designated 

 the 'inner tube' which arises within the proximal end of the 

 outer tube. As will be recalled, this. region of the original invagi- 

 nation is marked by a cluster of cilia-like processes which extend 

 into the cavity. Even in the stage represented by figure 21 the 

 surface of the cell is here thickened. In later stages this thicken- 

 ing becomes more extensive and finally develops into a deeply 

 staining ring-like elevation which projects from the bottom of 

 the outer tube and which bears a circlet of delicate threads (figs. 

 24, 25 and 26). 



At about the time the outer tube reaches a condition of maxi- 

 mum extension this ring begins to project into its cavity (fig. 

 27). This is the beginning of the formation of the inner tube 

 (i.t.) which continues to advance within the outer, as shown in 

 figures 28 and 29, until both tubes reach approximately the 

 same length (fig. 30) . As a matter of fact the inner tube grows 

 at the expense of the outer, for during its formation the length 

 of the developing spermatozoon is reduced about one-half, as 

 will be seen from a comparison of figures 27 and 30, and as is 

 shown in text-figure 1. As the head of the inner tube advances, 



