THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 449 



entering into a -detailed discussion of the "histogenetic" view of 

 the mitochondria, it may be said that the evidence is far from 

 being convincing. From what we know of the chemical nature 

 of the mitochondria, it becomes difficult to understand how 

 they may become transformed into structures so different 

 chemically. According to Cowdry ('16, p. 435), "it is apparent 

 that the doctrine of an actual chemical transformation of mito- 

 chondria into substances of diverse constitution is weak." 



As to the chemical nature of the mitochondria, practically all 

 workers agree that they are combinations of lipins with varying 

 amounts of albumin (phospholipins). The transformation of 

 the mitochondria into the yolk-spherules of the egg at once 

 indicates their lecithin nature. N. H. Cowdry ('17) has given 

 a summary of the more important data bearing upon the chemical 

 nature of the mitochondria. Lowschin ('13) has been able to 

 make mitochondria artificially in lecithin and albumin solutions. 

 These mitochondria behave in every way (form, solubility, 

 fixation and staining) like true mitochondria of organic cells. 

 Russo ('12) has described an increase in the number of mito- 

 chondria of the oocytes of the fowl following injections of 

 solutions of lecithin. 



While we are beginning to know something about the chemical 

 nature of the mitochondria, we are far from knowing their role 

 in the physiology of the cell. That they bear an important 

 relation to metabolism is conceded by many workers, and the 

 class of chemical compounds to which the mitochondria are allied 

 chemically (the lipins) have recently been emphasized in bio- 

 chemical works as being intimately concerned in metabolic 

 processes. In fact, Mathews ('15) believes that the phospho- 

 lipins are the most important substances in organic matter. 



In the oocytes of Cicada it is quite clear that the mitochondria 

 are related to the nutritive metabolic processes and that they are 

 actually transformed portions of the products of assimilation. 

 According to Cowdry ('17), in plants the "mitochondria are 

 concerned in the formation of chlorophyll, and thus the very 

 existence of the plant depends upon them." Maclean ('18) fed 

 one group of hens on a normal diet and another group on a diet 

 free from fats and lipins and concluded that the "lipins play an 



