EMBRYOLOGY OF COCCIDS 121 



11. SUMMARY 



1. The three ovarian elements, namely, the nurse cells, the 

 egg cell, and the follicular epithelial cells, are derived from the 

 primordial germ cells. All germ cells are exactly alike during 

 the oogonial period. The first differentiation begins after the 

 next to the last oogonial division. Few peripheral cells undergo 

 the last oogonial mitosis and enter into the so-called growth 

 period of the oocyte of the first order. Their nuclei are, at first, 

 condensed near one pole, but later become thread-like. At this 

 point another change occurs: three or four out of a group of four 

 (Icerya), or -five (Pseudococcus and Lecaniodiaspis) oocytes 

 situated peripherally overgrow the single cell situated at the 

 proximal end and secrete a sort of nutritive substance. At the 

 same time their nuclear contents become granular. These are 

 the nurse cells, while the single cell situated at the posterior end 

 becomes the true egg cell. The follicular epithelial cells, which 

 invest the nurse and the egg cells are oogonial cells that happened 

 to be at the proximal part of the group. These epithelial cells 

 multiply, like the somatic cells, by ordinary mitosis and their 

 nuclear contents do not assume the appearance of either a con- 

 densed or paired condition. 



2. The ovarian egg, at the time of its passage into the oviduct 

 consists of the following parts: a chorion, yolk membrane, cyto- 

 plasm, germinal vesicle with its nuclear membrane and contents, 

 and a colony of symbiotic organisms. In addition to these, the 

 eggs of Icerya and Pseudococcus contain fat granules and yolk- 

 like substance. 



3. All cleavage cells divide mitotically. No case of amitosis 

 occurs. Some of the cleavage cells later migrate to the peripheral 

 cortical layer and become the so-called blastoderm, while the 

 rest of them remain within the egg and become the so-called yolk 

 cells. The first cleavage spindle lies at right angles to the shorter 

 axis of the egg and the place where the cleavage cell first reaches 

 the cortical layer is at the posterior pole of the egg. 



4. The process of ventral plate formation is the so-called in- 

 vagination type. The invagination occurs at a short distance 

 ventrad to the posterior end of the egg. It is, at first, a shallow 



