VH] MITOCHONDRIA 97 



derived from their centres. The filament then arranges 

 itself in a coil or spiral, and gives rise to the " mitochondrial 

 spireme" ("macromitosome"), a conspicuous body lying 

 immediately behind the nucleus of the now elongating 

 spermatid. As the spermatid lengthens to form the sper- 

 matozoon, the macromitosome is drawn out and wrapped 

 round the axial filament, but it becomes so attenuated that 

 it could not be determined whether it remained as a final 

 constituent of the tail. 



In a number of Molluscs examined GATENBY finds the 

 behaviour of the mitochondria in spermatogenesis to differ 

 only in detail from that observed in Lepidoptera, with the 

 exception that no mitochondrial spireme or macromito- 

 some is formed, and the mitochondria pass as small vesicles 

 into the tail of the spermatozoon. He describes, however, 

 two other kinds of cytoplasmic bodies to which reference 

 must be made. The first of these he names micro-mitochon- 

 dria ; they differ from the larger "macro-mitochondria" not 

 only in their smaller size but also in always forming a 

 sheath round the proximal end of the axial filament. Since 

 in some species there is no difference in size, although the 

 mitochondria become separated into proximal and distal 

 groups, these bodies probably differ little from true mito- 

 chondria. In some forms (for example the slug Arion) 

 "post-nuclear granules" are also found. These granules 

 differ from mitochondria in staining like chromatin with 

 certain aniline dyes (toluidin blue); they appear in the 

 spermatocytes in the neighbourhood of the nucleus, and 

 form a dense ring just behind it in the spermatid. A third 

 body, often known as the "Nebenkern," which is conspicu- 

 ous in Molluscs, will be referred to below. 



Some writers have ascribed great importance to the mito- 

 chondrial bodies as a whole, and have supposed especially 

 D.C. 7 



