22 



CELL ORGANS 



[CH. 



wide-spread, occurring in cells of many kinds, especially in 

 embryos but also in adult animals. Their nature and be- 

 haviour will be described more fully in the chapter on 

 spermatogenesis, but in consequence of the great morpho- 

 logical and physiological importance that has been ascribed 

 to them by some writers, some reference to them is required 

 here. They consist of granules, rods or sometimes vesicles 

 which occur usually in a more or less compact group in the 

 neighbourhood of the nucleus. The extent to which they 



FIG. i . Mitochondria in the spermatogenesis of Blaps, 

 after DUESBERG (1910). 



a. Spermatogonium with scattered granular mitochondria. 



b. Spermatocyte ; mitochondria becoming rod-shaped. 



c. First spermatocyte division, mitochondrial rods becoming drawn 

 out around spindle. 



are developed varies largely not only in cells of different 

 kinds, but also in the same cell in different stages of its 

 growth. When the cell divides, the mitochondrial bodies are 

 either separated into the two daughter cells, or, according 

 to some observers, undergo division so that the parts are 

 divided into the two cells. The study of mitochondria is 

 less easy than that of the nuclear constituents of the cell 

 from the fact that they are injured or destroyed by many 

 of the fixatives commonly employed, especially those con- 

 taining acetic acid, and they also require careful staining 



