600 GEORGE T. HARGITT 



are, without doubt, chemical changes occurring, probably also 

 physical ones, and these would of course be more or less definite 

 and precise, even though they might not be visible. 



OOCYTES 



From this period up to the completion of the maturation 

 process there is no break and no uncertainty regarding the 

 changes or the order in which they occur. From the condition 

 in figure 2 up to the formation of the completely matured egg 

 the changes are briefly as follows: there is a gradual vacuolation 

 of the cytoplasm leading to the characteristic alveolar arrange- 

 ment, and a gradual condensation of the chromatin which ulti- 

 mately produces the haploid number of chromosomes of the 

 maturation mitoses. These changes will be followed more in 

 detail. 



Cytoplas?n. The cytoplasm of oogonia (figs. 2 to 6) in fixed 

 material is finely granular, closely packed, evenly distributed, 

 and stains rather deeply. As the oocyte is formed and begins 

 its growth, the cytoplasm may become slightly vacuolated (figs. 

 7 to 9) with the granules less closely packed and not staining so 

 deeply. As a rule, however, in oocytes which have just started 

 their growth there is little vacuolation of the cytoplasm and 

 these cells differ mainly in a lighter appearance in stained sec- 

 tions. There comes a time after growth is well under way when 

 the cytoplasm begins to assume the alveolar arrangement char- 

 acteristic of large ova. Usually this vacuolation begins in the 

 cell on the side away from the eccentric nucleus (fig. 10) and the 

 vacuoles commonly possess the central kernel shown in the 

 figure. 



The cause of this vacuolation may be the segregation of the 

 less dense substances of the cytoplasm, but the nucleus seems to 

 exercise some control over the process. Figure 9 shows what is 

 sometimes found, viz., a liberation of substances from the 

 nucleus which cause a liquefaction of the cytoplasm about them. 

 This is very evident in figure 11, \vhere deeply staining granules 

 are present in the center of each of the larger vacuoles of the 

 cytoplasm. It is not at all clear whether nuclear substances 



