MITOCHONDRIA IN GERM -CELLS 131 



and Cannon, the spireme of Gatenby does not seem wholly 

 explicable. 



Gatenby in 1922 described the very remarkable formation of 

 tail sheaths in Saccocirrus from the Nebenkern (33). This occurs 

 entirely during spermateleosis. The mitochondria composing the 

 Nebenkern run together to form larger and larger droplets, until 

 finally three sub-equal large spheres are formed. These elongate 

 tremendously and form the tail sheath. In this case there is no 

 division into inner and outer parts or any complicated formation 

 of secondary vacuoles such as that described by Bowen in the 

 case of the Hemiptera. 



So far then all that can be said of the mitochondria in spermato- 

 genesis is that they appear to metamorphose either directly or 

 indirectly into the tail sheaths when the latter are present. As 

 to the function of the tail sheaths or how they are actually 

 produced nothing is known. 



In the process of oogenesis and particularly of vitellogenesis, 

 the part played by the mitochondria is again in considerable 

 doubt. The general behaviour of the mitochondria may be fairly 

 briefly summarised. In most cases the mitochondria are either 

 invisible or else few in number and more or less scattered in the 

 oogonial stage. As the oocyte enters upon the growth period, 

 the mitochondria appear to clump themselves together and form 

 what has frequently been termed a " yolk nucleus." (N.B. — 

 This term has often been applied to structures other than 

 mitochondrial.) This usually breaks up sooner or later, and the 

 mitochondria are found to be fairly evenly distributed. 



On the whole the general opinion is that the mitochondria do 

 not metamorphose into yolk and that they do not appear to take 

 any direct part in vitellogenesis. As an example may be taken 

 the oogenesis of Lumbricus, described by Harvey (44) and by 

 Gatenby and Nath (39). These observers differ fundamentally 

 on several points, but they agree that the so-called yolk-nucleus 

 is formed of mitochondria. Harvey says they are filamentous, 

 while Gatenby and Nath describe them as granular, attributing 

 the filamentous condition to artefacts. They also agree that the 

 mitochondria are not metamorphosed into yolk. Similar con- 

 s—a 



