190 Dr. L. Doncaster. Gametogenesis and 



completion of the maturation divisions, remain separate and distinct, in some 

 cases until the second or third segmentation division of the zygote nucleus, 

 while in other eggs they become clumped together quite early, and cease 

 to be distinguishable in the segmentation divisions. To some extent this 

 difference does appear to be characteristic of the eggs of some females, but it 

 is by no means regular, and I think it cannot be regarded as a really 

 distinguishing feature. 



A second difference in the maturation of eggs laid by different females is 

 found at an earlier stage, but it is difficult to say whether it is really 

 significant. In all cases the nucleus before maturation comes to the surface 

 of the egg, when it is small and evenly stained, and is usually, perhaps always, 

 flattened for a time against the edge of the egg.* The nucleus then enlarges, 

 and its subsequent behaviour seems to show differences in the eggs of different 

 females. The differences between the two types will be described briefly, 

 before giving a more detailed account of the maturation processes. In the 

 eggs of some females it becomes top-shaped, or like two cones attached to 

 each other by their bases, the points of the cones being in a line perpendicular 

 to the surface of the egg (Plate 6, Figs. I, 1 and 2 ; II, 1 and 2 ; III, 1). As 

 the nucleus assumes this form, the chromatin becomes concentrated chiefly at 

 the inner and outer points, but there is often also a single or double ring of 

 granules round the equator, or common base of the two cones, which give the 

 appearance of chromatin emitted from the nucleus. In the subsequent stages 

 of these eggs, as will be described more fully below, the separation of the 

 chromosomes which will form the egg-nucleus from the inner polar 

 chromosomes occurs almost simultaneously with the division of the outer 

 group of polar chromosomes, with the result that as a rule three quite 

 distinct groups of polar chromosomes are formed (Figs. Ill, 7 ; IV, 5 and 6). 



In eggs of other females the process seems to be slightly different. The 

 nucleus appears never to assume the top-shaped form, but swells up into a 

 spherical nucleus containing a well marked reticulum, sometimes with 

 laro-er awregations of chromatin at the outer side or round its equator 

 (Plate 7, Figs. VII, 1 ; VIII, 1). In the later stages of these eggs the 

 separation of the innermost group of chromosomes, which sink in to form 

 the egg nucleus, appears to take place considerably before the division of the 

 outer group, and the latter division is apparently often incomplete, so that 

 only two groups of polar chromosomes may be found in the later stages. 



It is not difficult to choose series of eggs of individual females (e.g., 

 Nos. Ill and VII, Plates 6 and 7) in which the differences described are 

 fairly pronounced, but on the other hand eggs of other females show figures 

 * Cf. Part II of this series, 'Roy. Soc. Proc.,' B, vol. 83, Plate 17, fig. 3. 



