564 VERA DANCHAKOFF 



only description of the structure of the eggs before and after 

 fertihzation will be given with rerefences to the limited data 

 found in the literature, which attempt to explain this marked 

 difference in the condition of the eggs during these stages. 



The most striking feature of a ripe but immature egg (fig. 1) 

 is the presence of a very large nucleus. This nucleus contains a 

 well developed large spherical nucleolus, which in different eggs 

 may exhibit various aspects. This concerns chiefly its staining 

 reaction, for sometimes it appears very homogeneous and in- 

 tensely basophilic; at other times it stains very lightly not only 

 with the azur but even with the iron-haematoxylin method. Its 

 substance appears highly refractive, what enables its easy iden- 

 tification in living or unstained preparations. Some of the 

 nucleoli, which gradually lose their basophilic reaction, manifest 

 a striking vacuolisation, the vacuoles being filled by a less baso- 

 philic substance. 



Besides the nucleolus, the nucleus contains a finely granular, 

 intensely staining mass, together with a few thin twisted fila- 

 ments, sometimes strongly basophilic, at other times hardly 

 recognizable. Do these filaments represent chromosomes? It 

 is difficult to determine. In the granular mass of the nucleus 

 some larger particles of intensely basophilic substance can also 

 be observed. 



The cytoplasm of an immature egg is not homogeneous. In 

 many places it appears denser and seems to contain peculiar 

 formations, not always very distinctly separated from the adja- 

 cent cytoplasm. They appear as strings and larger ribbons or 

 broken masses (fig. 1), and evidently correspond to the large 

 mitochondria of insect spermatogonia, which were kindly demon- 

 strated to me by Prof. McClung and Miss Brockett. 



At this stage the egg does not present any other definite 

 structures — there is no trace of a centresome, centrioles, or 

 chromidia. However, the egg presents at its periphery two dis- 

 tinct layers, both separated from the rest of cytoplasm by more 

 or less precise boundaries. These layers are not always easily 

 discernible and are exempt of any definite morphological struc- 

 ture. The outer layer is very homogeneous, the inner layer is 



