130 ZOOLOGY 



(Bowen, 4). During spermateleosis they appear to undergo very 

 extraordinary changes. They first of all collect into a mass on the 

 side of the nucleus on which the centrioles now lie. This mass is 

 termed the Nebenkern (Fig. 64, D). The subsequent history varies 

 somewhat, and it is not possible to make a connected description. 

 Doncaster and Cannon (20, 26), in 1920, working on the louse, state 

 that the granular mitochondria become vacuolated so that the 

 Nebenkern appears as a mass of foam. The outer vesicles fuse to 

 form larger ones. This process continues until near the spermato- 

 cyte division the outer vesicles have become only two in number 

 and hemispherical in shape. Inside there is a mass of more deeply- 

 staining vacuoles. After the unequal division of the cell the mass 

 moves back into the mass of protoplasm gathering on the tail, but 

 was not actually seen to be sloughed off owing to technical diffi- 

 culties. They further emphasised that the so-called mitochondrial 

 spireme seen by Gatenby in the Nebenkern was due to optical 

 section of the vacuoles in the inner mass. 



Bowen returns to this point in a paper (7) in 1922. He conceived 

 the typical Nebenkern to consist of two parts. The outer, or 

 chromophobic, is derived from the medullar of the original mito- 

 chondria forming the mass ; the inner, or chromophilic, is from the 

 cortex of the mitochondria (Fig. 64, D, E). He does not explain how 

 the readjustment necessary to produce this condition is obtained. 

 However, he considers the inner chromophilic mass to exist in many 

 forms. For instance, it may be in spiremes in the Lepidoptera 

 (Gatenby, 30a), or as plates in the Hemiptera (Bowen). Eventu- 

 ally the whole central mass disappears in the Hemiptera, although 

 as this takes place faintly-staining vacuoles appear within the 

 chromophobic outer vesicles. These vacuoles, by coalescence, 

 form the core of the tail sheaths (Fig. 64, F, G). 



Bowen insists that very varied techniques should be used 

 in problems such as these, so that only the best preparations 

 — those considered most nearly to conform to the condition in 

 the living cell — are used. This really only moves the problem 

 a step further in a circular direction, and although his own 

 platework in the Hemiptera may correspond essentially with 

 the mass of vacuoles (vacuolated platework ?) of Doncaster 



