THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 443 



perinuclear zone may become massed about the centrosome, 

 forming the compact "corps de Balbiani" which later disinte- 

 grates in the formation of yolk (as in the Arachnids, etc.). 



(b) Origin of the Mitochondria. There are two facts of im- 

 portance to be noted in the foregoing discussion: (i) the quite 

 usual presence of mitochondria in a zone of the cytoplasm im- 

 mediately surrounding the nucleus; (2) the presence of this 

 perinuclear zone at a time when the mitochondria are increasing 

 greatly in number. One of the most important questions bearing 

 on the nature and role of the mitochondria is bound up with the 

 mode of their origin and increase in number, and there has been 

 considerable controversy regarding these questions. According 

 to the view of Meves, Bouin, Duesberg and others, the mito- 

 chondria have no "de novo" origin, but are always derived from 

 pre-existing mitochondria by a process of division. The chief 

 evidences to support this view are: (i) the constant presence of 

 mitochondria in all cells at all times; (2) the mitochondria within 

 the cell are actually distributed to the daughter cells at the time 

 of mitosis; (3) in some few cases (Meves in Ascaris, Duesberg in 

 Ciona and Apis) the mitochondria of the fertilized egg have 

 been traced into the embryonic cells. In the first place, it may 

 be said that the omnipresence of mitochondria in all living cells 

 may be interpreted upon an entirely different basis as I shall 

 attempt to show later. There is, of course, a genetic continuity 

 of mitochondria to a certain degree; the mitochondria of a cell 

 are certainly carried into the daughter cells at the time of 

 mitosis, but the view that individual mitochondria give rise to 

 "homologous" mitochondria of succeeding cell-generations is 

 entirely without evidence. Duesberg ('18) found that the yellow 

 ooplasm of the Ascidian egg was rich in mitochondria, and, using 

 the results of Conklin ('05) who traced yellow ooplasm of the egg 

 into the embryo, consequently maintained that the mitochondria 

 were genetically continuous from the fertilized egg to the em- 

 bryonic cells. While there is no question that the yellow ooplasm 

 is continuous, yet this is far from establishing that the individual 

 mitochondria are continuous. 



Opposed to the "genetic continuity" hypothesis of the mito- 

 chondria, we have the "chromidial" hypothesis developed by 



