GERM CELLS IN THE ARTHROPODA 159 



but soon after it reaches a sphere-like shape it begins 

 to vacuolate and becomes irregular (Figs. 46, K ; 47). 

 It also seems probable that in some obcytes the 

 ob'cyte spindle gives rise to the keimbahn-chromatin, 

 whereas in others it becomes disorganized, forming 

 the nucleus of the egg (Fig. 47, A, B, C). What 

 causes the difference in the history of the ob'cyte 

 spindles ? No definite answer can be given to this 

 question, but there are two possibilities, (1) external 

 and (2) internal influences. It seems very improb- 

 able that any internal mechanism exists which 

 determines what the history of the oocyte spindle 

 shall be. On the other hand, the arrangement of 

 the oocytes in the ovary might cause the spindle of 

 those most posteriorly situated to become keimbahn- 

 chromatin and of those next in order to transform 

 into nuclei. According to this view the oocytes de- 

 pend upon chance for their final position in the 

 ovary, and the fate of the spindle is decided by the 

 environment of the oocyte. 



There are numerous cases of cell fusion in both 

 PROTOZOA and METAZOA, and germ cells and somatic 

 cells. For example, PROTOZOA engulf other cells ; 

 the fully grown ova of Hydra consist of several 

 germ cells fused together; and leucocytes may fuse 

 with one another. In all such cases the nucleus of 

 one cell persists, whereas those of the other cells 

 disintegrate and disappear. Among certain leuco- 

 cytes of Axolotl, however, Walker (1907) has de- 

 scribed a sort of fusion which results in the trans- 

 ference of the chromatin from one cell to another 



