1909.] Gametogenesis of the Gall-Fly, etc. 97 



In eggs preserved very shortly after being laid, the nucleus appears as a 

 small darkly-stained body, either flattened against the edge of the egg or 

 somewhat spindle shaped, with the longer axis of the spindle perpendicular to 

 the edge. There is little doubt that the very narrow flattened nucleus is the 

 earlier stage, but as both are found in eggs within half an hour of being laid, 

 this is not perfectly certain. The nucleus now begins to enlarge, and instead 

 of staining deeply and almost evenly throughout, chromatin bodies connected 

 more or less conspicuously by a network appear within it (fig. 23). The 

 succeeding stages are somewhat obscure, and are not unlike the maturation 

 processes described by Henking* in the Gall-fly lihodites rosw. The nuclear 

 membrane becomes faint and disappears, and the chromatin bodies segregate 

 themselves to some extent into an inner and outer group, but whether 

 by division of the individual chromosomes, or by a separation of chromo- 

 somes previously distinct, I cannot be sure (Plate 2, figs. 22, 24, 27, 

 30). The chromosomes of the inner, group then separate themselves 

 from those of the outer, and in so doing take the form of rods 

 lying side by side or with their inner ends converging somewhat as in 

 the anaphase of a typical mitosis (Plate 2, fig. 30). The outer part of 

 the nucleus meanwhile has never become clearly separated into chromo- 

 somes, but appears as a group of chromatin bodies connected together 

 by strands as in a reticular nucleus. Although Henking does not figure a 

 stage exactly of this kind in lihodites, yet he describes something similar. 

 On pp. 149 and 150 he writes : " Die untere Tochterplatte lasst die Neunzahl 

 unschwer erkennen, wahrend in der ausseren Tochterplatte wiederum eine 

 theilweise Verklebung eingetreten ist." In a nuclear division of this kind, 

 in which there is never an equatorial plate, and in which the chromosomes of 

 one half never become clearly separated, it is not easy to determine the 

 chromosome number with certainty. But from a comparison of a large 

 number of sections, especially when cut tangentially to the egg, it is fairly 

 clear that the number of chromosomes in the inner group is about ten. In 

 some sections not so many are visible, but that the number is really approxi- 

 mately ten there can be no doubt, i.e. the same number as in the spermato- 

 cyte divisions already described. In lihodites Henking found nine. 



The division just described does not lead to the production of two 

 resting nuclei, but is succeeded immediately by further changes, which here 

 also are obscure and hard to follow. Henking says that in lihodites the 

 chromosomes at each end of the first division-figure again divide, and thus 

 give rise to four groups, of which the innermost forms a definite nucleus 

 which sinks in as the female pronucleus, while the other three remain near 

 * ' Zeit. Wiss. Zoo.,' vol. 54, 1892, p. 147. 



