84 GEORGO ORIHAY SHINJI 



and follicular epithelial cells are regarded as abortive cells. No 

 differential mitosis was observed. 



Hegner ('12) states that the germ cells in Miaster give rise to 

 nothing but the true oocytes, and that the nurse cells and 

 epithelial cells are both derived from somatic cells. He deduces 

 this from the fact that in Miaster americana altogether sixty- 

 four oogonial cells are formed by six successive divisions of a 

 single primordial germ cell and that the number of the young 

 larvae produced is also about sixty-four. 



The foregoing survey of the more important literature per- 

 taining to this subject, brief as it is, indicates that, even among 

 the same order of insects, there is no definite law governing the 

 differentiation of the three ovarian elements. The accounts of 

 the lineage of the ovarian elements in Leptinotarsa (Wieman, '14; 

 Hegner, '12), and Hydrophilus (Korschelt, '89) are good ex- 

 amples. However, it should be mentioned that in all insects 

 the oocytes and also the nurse cells, when present, are all 

 derived from primordial germ cells. As yet no case has been 

 found in which the primordial germ cells of the insects entirely 

 degenerate and the secondary or functional germ cells are formed 

 de novo at a much later period of development. 



3. THE EGG 



The eggs of all species of coccids studied, at the stage last 

 mentioned, consist of the following substances : 



1. Chorion — the outermost covering or membrane. 



2. Protoplasm — the ground substance. 



3. Corticular layer — a thick protoplasmic layer next to the 

 chorion. 



4. Fat globules — oily droplets suspended in the protoplasmic 

 network. 



5. Yolk granules — protoplasmic suspension. 



6. Pigment oil-fluid filling interspace between fat globules. 



7. Germinal vesicle with its nuclear membrane. 



8. Yolk membrane — membrane next to, and, in fact, almost 

 apposed to the chorion. 



