Maturation of Parthenogenetic and Sexual Eggs 139 



taining eggs were killed and fixed in masses of thousands and 

 sectioned in toto. Many eggs were found in the desired stages, 

 but as the eggs are filled with yolk granules of various sizes it was 

 exceedingly difficult to find many sections in which the yolk 

 granules were not mingled with the chromosomes. 



Hot sublimate acetic, Bouin's fluid, strong Flemming, Gilson, 

 Carnoy, and alcohol acetic, were used as killing and fixing fluids. 

 Some good preparations were obtained by each method, but 

 alcohol acetic gave the best results in obtaining equatorial plates; 

 for it coagulated the cytoplasm of the egg in such a way as to 

 embed the yolk granules in its meshes, thus leaving the spindle 

 and its chromosomes free from yolk granules. Thousands of 

 animals were sectioned and about three hundred good slides were 

 made. Sections were cut 5/z in thickness in 51° to 52° C. paraffine. 



Many parthenogenetic females were also isolated separately 

 and the sex of their off"spring determined, for those eggs first laid, 

 before the females were killed and sectioned. The general nature 

 of the maturation stages of such eggs was determined before a 

 more detailed study was made of the eggs in the mixed slides. 



After the eggs are laid the envelope around them is so thin and 

 at the same time so exceedingly impervious to fixing fluids that 

 the eggs usually collapse in the process of fixation. Sometimes a 

 few do not collapse in alcohol acetic but, however careful one 

 may be, by the time the eggs are embedded they have shrunken. 

 In such eggs the yolk granules are so crowded in among the 

 chromosomes and stain so darkly that no satisfactory results can 

 be obtained. 



In order to free the spindle from these granules the eggs were 

 first centrifuged. In sections of such eggs the maturation spindle 

 remained in the clear middle zone of the egg and was often entirely 

 free from yolk granules. As only a few sections of these eggs 

 were made no good stages were found in which the chromosomes 

 could be counted but the method gives promise of results that can 

 not be obtained in other ways. 



Heidenhain's iron haematoxylin was used chiefly and gave the 

 best results although many other stains were tried. 



In order to see the polar bodies the eggs, some time after they 



