102 CYTOPLASMIC STRUCTURES [CH. 



protoplasm known as the idiozome, but in Lepidoptera 

 from rod-like bodies belonging to the Golgi apparatus, which 

 become vesicular, coalesce around the nucleus, and produce 

 the acrosome. The centrosome of the spermatid sinks in to 

 the neighbourhood of the nucleus, grows out a long filament 

 which forms the axial fibre of the tail, while the centrosome 

 itself is the chief constituent of the middle-piece. In the 

 primary spermatocyte, and sometimes earlier, mitochon- 

 drial granules appear as a cloud around the nucleus; they 

 multiply, enlarge, become vesicular, and (possibly in con- 

 sequence of defective fixation) may coalesce into strands. 

 They become passively distributed during cell division, and 

 in the spermatid either unite to form a definite "mitosome," 

 or may remain as a compact group of vesicles. As the 

 spermatid elongates, the mitochondrial mass is drawn out 

 and forms a sheath around the axial filament of the middle- 

 piece and tail. Whether it is carried into the egg, or becomes 

 absorbed, or, as has been maintained in at least one case, 

 thrown off, appears to vary in different animals. In addition 

 to the mitochondria, various other bodies have been de- 

 scribed, the nature of which is not less obscure. The chief 

 of these is the so-called "Nebenkern," which seems, like the 

 acrosome, to be derived from the Golgi apparatus and to be 

 closely connected with the "idiozome" of MEVES a body 

 probably identical with GATENBY'S "archoplasm." For the 

 fuller elucidation of the origin and fate of these structures, 

 it seems clear that improvements in the technique of fixing 

 and staining are essential. It should be noted that at least 

 both mitochondria and Golgi apparatus also occur in the 

 early stages of the developing egg and maybe very abundant 

 in the mature egg, but our knowledge of the finer details of 

 oogenesis is even more defective than that of the develop- 

 ment of the spermatozoon. 



