GERM CELLS OF ARGAS 647 



nuclear bodies.' A very distinct 'zwischenkorper' (not shown 

 in figure 9) lies against the wall of the cell, the striated layer 

 here being broken. No centrosomes are visible. The nucleus 

 shows one (sometimes two or more) true nucleoli, and one chro- 

 matin nucleolus. At this stage the chromatin is diffuse in 

 arrangement. 



Turning now to earlier stages it will be noted that the true 

 mitochondria are distinctly seen in spermatogonial cells before 

 the beginning of the growth period (fig. 1). Indeed, these gran- 

 ules may be distinguished in stages much earlier than those 

 represented. Following the last spermatogonial divisions, the 

 mitochondria aggregate more densely in certain regions of the 

 cell, more particularly against the nuclear wall (figs. 2 and 3) 

 where they form one or more deeply staining caps. Thus far 

 in development the cytoplasm appears entirely homogeneous 

 except for the presence of mitochondria. Within the nucleus 

 two nucleoli appear shortly after the end of the last sperma- 

 togonial division, and the chromatic material, which is at first 

 diffuse, is more distinctly localized (fig. 3). Figure 4 marks the 

 first appearance of extra-nuclear bodies and vesicular bodies. 

 The former stain red with Bensely's acid fuchsin and are located 

 both within and without the nucleus, many of them being in 

 close contact with the nuclear wall. The latter are now in the 

 form of short fibers, at first very difficult to resolve, but later 

 increasing in bulk and becoming fusiform. They take the 

 counter stain. 



In figures 5, 6, 7 and 8, representing successive periods in the 

 growth of the cell, the extra-nuclear bodies become more widely 

 scattered in the cytoplasm. The vesicular bodies increase in 

 number and are changing in form from the fusiform fibers of an 

 earlier stage to the vesicular condition which they will retain 

 until their disappearance. The mitochondria are more numer- 

 ous and are evenly distributed throughout the cytoplasm. The 

 genesis of the striated outer layer is seen in figure 7. At the 

 end of the growth period (fig. 9) the striated layer has increased 

 in thickness, the mitochondria maintain their uniform distribu- 



