140 Harry Lewis Wieman. 



chamber, into a thin epithelial layer closely applied to the tunica 

 propria. Everything indicates that the peritoneal sheath with 

 its muscular investment, which is inserted into the dorsal body 

 wall, serves to support the ovarioles. 



However vestigial its structure in the adult, in the larval and 

 pupal periods the terminal thread is of considerable impor- 

 tance in producing the epithelial cells of the end chamber that 

 later play an important part in the development of the egg. 

 Whether or not it has, during the larval and pupal periods, the 

 function ascribed to it by Heymons, I am not prepared to say, 

 since this is a point that can not be readily demonstrated one 

 way or the other. 



It will be noticed in Figs. 5 and 38, that the chromatin of the 

 germ cells has a peculiar granular appearance that is quite dif- 

 ferent from the reticular structure of the nuclei of the germ cells 

 at the lower end of the tube (Fig. 6) . This is the first indication 

 of the differentiation of the germ cells into functional sexual cells 

 that will develop into eggs, and nurse cells. 



The question immediately arises as to what causes this differ- 

 entiation. Giardina ('01) described in Dytiscus marginalis a 

 process of differentiation in which one of the daughter nuclei, re- 

 sulting from the division of a primordial germ cell, receives in ad- 

 dition to the usual number of chromosomes, a certain amount of 

 chromatin, and develops into a functional germ cell ; whereas, the 

 other daughter cell lacking this extra chromatin becomes a nurse 

 cell. Nothing of this kind is to be observed in L. signaticollis. 



At just about this time in the developmental history, there oc- 

 curs at the junction of the terminal chamber and tube stalk a 

 transformation that is significant in this regard. Fig. 6 shows the 

 condition immediately preceding the change; the boundary be- 

 tween the egg chamber and the tube stalk is sharp, and the cells 

 of the latter can be distinguished from the epithelial cells not only 

 by their shape, but by the capacity of the cytoplasm to stain more 

 deeply. Fig. 7, which is a few days older, shows a pale, lightly 

 staining, semi-fluid mass that blends with the epithelial cells on 

 the one hand and the cells of the ovariole stalk on the other. It 

 is very difficult, impossible in some cases, to make out cell bound- 



