194 Dr. L. Doncaster. Gametogenesis and 



shows the polar chromosomes of an egg of this series after the maturation 

 divisions are completed ; there is a compact mass derived from the outer 

 half of the inner group (on the right of VII, 8, a, with three pieces extending 

 into the section 8, b), while the halves of the outer group are intermingled 

 in an irregular mass extending through the two sections. As in the case of 

 the earlier stages, however, various intermediate conditions occur between 

 such figures as VII, 8, and III, 7, and it is possible that the two kinds of 

 eggs described are rather the extremes of a continuous series than sharply 

 distinct types which might be correlated with a difference in sex-production 

 in the flies to which they give rise. 



One other point should be noted. In several figures {e.g., VI, 7 ; VII, 7) 

 there is a more or less conspicuous lagging chromosome, which is possibly 

 derived from one of the chromatin strands which may connect the inner and 

 outer groups after the first division (Figs. X, 1, 2 ; VI, 5). I have not been 

 able to find any regularity in its occurrence, but if one chromosome differs 

 from the rest in tending to lag in division, the presence of this chromosome 

 in the iuner or outer group might possibly be the differentiating factor which 

 determines whether the egg becomes a male-producing or female-producing 

 individual. 



The type of mitotic figure described, which occurs in the maturation 

 division of both the sexual and parthenogenetic eggs of Neuroterios, and 

 which is very similar to that described by Henking* in another Cynipid, 

 Bhodites, is so different from that commonly found in nearly all other 

 organisms that some further discussion of its peculiarities seems needed. 

 An obvious suggestion is that it is due to defective preservation, and this 

 explanation is supported by the fact that the state of preservation of the 

 eggs seems to differ considerably in eggs fixed together in the same tube. 

 But on the other hand there are strong reasons for believing that this is not 

 the true, or at least not a complete, explanation. 



In the first place quite similar figures are found in eggs fixed with 

 Petrunkewitsch's fluid and Gilson's acetic alcohol sublimate, both of which, 

 however, are of similar constitution, but are very different from the fixatives 

 (hot water and Flemming's fluid) employed by Henking. More important 

 reasons for believing that the peculiarities observed are not due to bad 

 fixation are (1) that quite normal and well-preserved segmentation mitoses 

 occur in rather older eggs, and (2), the beautiful clearness and regularity of 

 the fine chromatin strands could hardly be produced by poor fixation. The 

 drawings give only an imperfect representation of the fineness and regularity 

 of the actual figures, owing to the difficulty of rendering them accurately in 

 * 1 Zeit. Wiss. Zool.,' vol. 54, p. 147 (1892). 



