THE GERM-CELLS OF CICADA (lIBICEN) SEPTEMDECIM. 445 



has hitherto been only occasionally expressed in the literature. 

 This is what might be called the "interaction theory," and 

 according to it the mitochondria are neither self-perpetuating 

 structures, nor are they derived from the chromatin of the 

 nucleus, nor by a disintegration of the sphere material. Accord- 

 ing to this view the mitochondria are cytoplasmic differentiations 

 which arise through specific chemical actions of the nucleus 

 upon materials in the cytoplasm. I have before emphasized 

 the almost universal presence of a particular zone of mitochondria 

 immediately surrounding the nucleus at certain times in the 

 cell-cycle, and I believe this perinuclear zone to be one of the 

 best morphological demonstrations of an "interaction" between 

 nucleus and cytoplasm. The presence of this perinuclear zone 

 of mitochondria during the period in the oocyte when the mito- 

 chondria are increasing in number as the cytoplasmic volume is 

 also growing by assimilation of products from the nurse-cells, 

 supports the view that the mitochondria are. being built up by 

 nuclear action on substances in the cytoplasm. After the maxi- 

 mum amount of mitochondria has been elaborated, the peri- 

 nuclear zone is dissipated and the mitochondria become diffusely 

 spread in the cytoplasm followed by their transformation into 

 yolk. 



Montgomery ('n) and Browne ('13) have also expressed views 

 that the mitochondria may arise as a result of the interaction 

 between nucleus and cytoplasm. 



The view of mitochondrial continuity has no more than weak 

 circumstantial evidence to support. Granting that the mito- 

 chondria of the spermatozoa are brought into the egg and that 

 the cells of the embryo and adult all possess mitochondria, it is 

 far from establishing the fact that the mitochondria of these 

 cells are derivable from those of previous cell-generations which 

 go back to the fertilized egg. Mitochondria do arise, as such, 

 de novo in the cells by the chemical actions of the nucleus on the 

 cytoplasm immediately surrounding it, although there may be 

 a limited amount of mitochondria carried over from the previous 

 cell-divisions. 



Just w r hat portion of the cytoplasm is acted upon by the nucleus 

 is another matter. In the oocytes of Cicada, nutriment is 



