Germ Cells of Leptinotarsa Signaticollis. 149 



unmistakable resemblance to those of the stalk in early stages 

 (Figs. 1, 2), whereas the epithelial cells are of a totally different 

 appearance. 



Both kinds of cells have their origin in the mesodermal somites 

 (Heymons '91, Wheeler '93), but the cells of the ovariole stalk 

 early undergo a differentiation which distinguishes them from the 

 epithelial cells. The former are columnar in outline and stain 

 deeply, while the latter are round or oval and show no affinity for 

 the stain. 



In the differentiation of the germ cells into egg and nurse cells, 

 we have a very good example of the general conclusion which 

 Whitman ('93), F. R. Lillie ('06), and others have reached ; that 

 morphogenic processes can not be conceived as merely the sum 

 total or the resultant of the individual cell activities, but that the 

 organism (the ovary in the present case) operates as a unit with- 

 out respect to cell boundaries. There is no reason for believing 

 that the primordial germ cells differ in nuclear contents ; neither 

 is there any evidence of a differentiating division of the chromatin 

 which would predetermine which of them were to become func- 

 tional ova and which nurse cells. On the contrary, the process 

 seems to be the result of the activity of several distinct cell ele- 

 ments which operate together as a whole. 



The Formation of the Egg Strings. 



The development of the egg string was first studied by Leydig 

 ('66), who regarded it as a portion of the protoplasm of the egg. 

 Its relation to the nurse cells does not seem to have been very 

 clear, especially in telotrophic ovarioles such as are present in 

 L. signaticollis. For a long time it was supposed that the eggs of 

 these forms were without egg strings and that the follicle cells 

 supphed the ovum with nutrition. Will ('85) gives a diagram (Fig. 

 11) showing the relation of the strings to the eggs in Nepa and 

 Notonecta that portrays the condition in my material, but he says 

 nothing about their formation or the nature of their connection 

 with the nurse cells. 



