64G D. B. CASTEEL 



germ cells is rendered difficult by the rapidity with which they 

 disintegrate after removal from the body of the tick. Even in 

 the most suitable medium, a modification of Lock's solution, 

 they remain normal for but a short time. 



HISTORY OF THE SPERMATOCYTES AND SPERMATIDS 



General account 



As a basis for a review of the developmental processes which 

 occur during the history of the germ cells of the tick it will be 

 well to consider first the composition of a spermatocyte which 

 is approaching the end of the growth period (fig. 9). The cell 

 exhibits a distinct outer layer (s.l.) well demarcated from the 

 underlying cytoplasm, composed of numerous excessively fine 

 striae perpendicular to the surface. A tangential section through 

 this layer or a surface view of the cell suggests the appearance of 

 a faceted compound eye or of honeycomb. This region is 

 referred to as the 'striated layer.' Between this area and the 

 nuclear wall are three distinctly different types of inclusions 

 within the otherwise homogeneous cytoplasm. The largest and 

 most conspicuous of these structures (v.b.) are vesicular or sub- 

 vesicular in form, some of them having the appearance of short- 

 ened cylinders, possibly open at the ends. In many respects 

 these bodies fulfill the requirements of mitochondria, but, since 

 they fail in certain particulars, they are here designated 'vesicular 

 bodies.' At this period they take the counter stain with Bensley's 

 acid-fuchsin-methyl-green or toluidum blue but may also show 

 a tinge of red. The true mitochondria (mi.) appear as numerous 

 minute granules well scattered throughout the cytoplasm. These 

 granules often show a linear arrangement although they do not 

 fuse to form distinct threads and they take the fuchsin stain. 

 The third type of inclusion is represented by a number of small 

 bodies (e.b.), much larger than the true mitochondria, which are 

 scattered irregularly in the cytoplasm and which take the red 

 of Bensley's stain. These structures vanish from the cytoplasm 

 when the stage represented by figure 9 is reached, but may be 

 seen in the five preceding figures. They are designated 'extra- 



