80 GEORGO ORIHAY SHINJI 



fixing fluids as well as ordinary water will kill and fix the specimen, 

 but in such a case the finer details of nuclear structure are often 

 destroyed or distorted. 



2. THE ORIGIN AND DIFFERENTIATION OF THE OVARIAN 

 ELEMENTS 



The germ cells in the ovaries of the larvae at the time of hatch- 

 ing are similar in size and appearance (fig. 1). By mitosis, these 

 germ cells multiply during the first, second, and third larval stages 

 and form a mass of so-called oogonia (fig. 6.) At an early period 

 in the fourth larval stage, however, all oogonia cease to multiply. 

 Consequently, all appear alike on account of their being in 

 the so-called resting stage. This condition is soon followed by 

 a peculiar phenomenon. A few oogonia situated along the 

 periphery of the ovary suddenly undergo another, the last, 

 oogonial division and begin to grow, not only in size, but also in 

 nuclear complexity. The number of these oocytes of the first 

 order forming a group varies with the species. In Pseudococcus 

 there are four oocytes in a group, but in Icerya the number is 

 five. At first the nuclei of the oocytes in each group appear 

 exactly the same, all being in the so-called synizesis stage (fig. 4) . 

 From the contracted nuclear contents fine thread-like chromo- 

 somes emerge (fig. 6). At first these chromosome threads are 

 distinctly doubled, but later appear as single. 



Meantime a sort of protoplasmic substance begins to be 

 secreted around each of the oocytes except the one situated 

 toward the proximal end. As their later history shows, these 

 secretory oocytes nourish the single oocytes located below or 

 toward the distal end, and thus become the so-called nurse cells. 

 The cytoplasm areas of the fast-growing nurse cells soon come 

 into contact with one another. Being colloidal in nature, the 

 nutritive substances secreted by the nurse cells elongate in the 

 direction of the least resistance, which in this case is toward the 

 egg nucleus, for the expanding force of the nurse cells is much 

 greater than that of a single egg cell situated near the distal end. 

 Consequently, the nutritive substance, which is elaborated by 

 the nurse cells, now literally pours over the egg, causing a rapid 

 increase in its size (fig. 11). 



