EMBRYOLOGY OF COCCIDS 83 



from the inner mass in common with the nurse cells or ovarian 

 glands, but grow out of the follicular epithelial cells at the base 

 of the end chamber. 



Balbiani ('82) states that the germ rudiments of partheno- 

 genetic aphids undergo a process of budding previous to their 

 differentiation into the nurse cells and oocytes. 



Mecznikow ('66) derived the end chamber from a mass of cells, 

 "Die am untersten Pole des endf aches liegenden Zell sich 

 bedeutend vergrossert, wobei sie in ein, aus dem Endfachepithel 

 entstandes Follikel eingeschlossen wird und hier ihre weitere 

 Entwicklung vollzieht. " 



Stevens ( '05) insists that the contents of the end chamber are 

 of two kinds, possibly corresponding to the summer and winter 

 eggs, and that those situated on the lower portion of the end 

 chamber degenerate in the ovaries which produce the agamic 

 eggs. 



In insects (other than Hemiptera) the results of several inves- 

 tigators differ with the species wdth which they have worked. 

 The prevailing idea, up to 1905, was that the three ovarian 

 elements, nurse cells, epithelial cells, and oocytes, are all derived 

 from the germ cells. Paulcke ('00) who studied the development 

 of the honey-bee, however, discovered for the first time that the 

 nurse cells and oocytes are originally the same, but later become 

 differentiated by a certain irregular cell division. Similar dis- 

 coveries of the existence of a quantitative difference between the 

 nurse ceils and oocytes have since been reported in several 

 Coleoptera. In Dytiscus, for example, Gunthert ('10) found 

 that the chromatin eliminated from the nucleus passes, in each 

 successive mitosis, into the pole of a single daughter cell, and 

 that the cell ha\dng this extra chromatin substance becomes the 

 oocyte and those lacking this the nurse cells. Somewhat similar 

 observations were made by Giardia ('01) and Debaisieux ('09) in 

 Dytiscus, and Govert ('13) in Carabus, Cicindela and Trichiosoma. 



The oogonial origin of the oocytes, nurse cells and follicular 

 epithelial cells was clearly established in Polistes and Platy- 

 phylax by Marshall ('07); in Podura by de Winter ('13), and in 

 Leptinotarsa by Hegner ('14). In these cases, the nurse cells 



