82 GEORGO ORIHAY SHINJI 



substance becomes compact, thereby causing an indentation of 

 the surface. 



In the next stage, the nuclear membrane of the germinal 

 vesicle disappears and the vesicle itself loses its clear appearance. 

 This change is due to the appearance of the spindle fibers about 

 the chromosomes (fig. 26). The oocyte is now in the metaphase 

 of the maturation division. Following this stage the chromo- 

 somes divide into two groups and move to the opposite poles. 

 Soon one of the daughter cells gradually protrudes from the egg 

 proper (fig. 31). In this manner the first polar body is formed. 

 The process of the second polar body formation has not been 

 studied, but that the egg undergoes the second maturation 

 division may be established by the presence of three polar bodies. 

 Meanwhile the epithelial cells not only cease to multiply, but 

 they also become reduced to a membranous structure. The 

 nurse cells also cease to grow. Their size becomes very much 

 reduced. The contents of the nurse chamber is withdrawn into 

 the egg and its epithelial layer shrinks to a small mass. This, 

 together with the remains of the epithelial cells of the egg, closes 

 over the opening left by the egg entering the oviduct. 



The earliest egg found in the oviduct (or the uterus, as it is 

 often called) shows a large nucleus at the center of the egg. Since 

 this large nucleus divides, it must be the first cleavage nucleus. 

 It follows, therefore, that the union of the male and the female 

 pronuclei must have occurred during the passage of the egg pro- 

 nucleus to the center of the egg after the formation of the last 

 polar body. 



Thus my observations on the three species of coccids are in 

 accord with those of Leuckart ('53) and Emeis ('16). It may 

 also be added that the ovary of Icerya purchasi is the most favor- 

 able material for the study of this problem, since the cells are 

 large and numerous. 



The origin of the three ovarian elements in aphids has been 

 differently described by different writers. Lubbock claims that 

 the egg and nurse cells are modified epithelial follicular cells of 

 the end chamber. Recent observations of Tannreuther ('07) are 

 to the same effect, for he declares that the egg cells do not arise 



