200 Gametogenesis and Sex-Determination in the Gall-Fly. 



little trace of division. The innermost group is in one section, the middle 

 group and most of the outer group in the next. The chromosomes of the 

 outermost group not in this section are represented below. 

 VII, 8. — Polar chromosomes after maturation is completed, in two successive 

 sections. There is a compact inner group of about 10, and an outer group 

 which contains approximately 20 chromosomes. 



Series VIII, 1. — " Spherical " type of nucleus with early stage of threads being drawn 

 out towards egg-centre. 

 VIII, 2. — Double maturation division. There appear to be more than 10 chromo- 

 somes in the inner group, and they seem to be in process of sorting out 

 rather than of division. The inner group is in one section ; the chromo- 

 somes of the outer group marked x in the next, and the rest of the outer 

 group in the next to these. 



Series IX, 1-6. — Six figures of early stages from eggs of various females, preserved with 

 Petrunkewitsch's solution in 1907, and showing strands or loops of 

 chromatin being drawn out towards both the egg-centre and egg- margin 

 from a nuclear reticulum. In IX, 6, the figure is seen obliquely, and is cut 

 in two sections ; the upper portion is the outer. 



Owing to the difficulty of interpreting and rendering structures seen in 

 perspective, the details of the reticulum as represented are not rigidly 

 accurate, nor is the whole thickness of the nucleus shown in every case. 



Series X.- — Five figures of eggs of various females, later than those shown in Series IX. 



X, 1. — Egg preserved in 1906 (Petrunkewitsch's fluid), showing chromatin 

 strands connecting the inner and outer groups. Eight chromosomes, most 

 of them clearly split longitudinally, are visible in the inner group ; it is 

 possible that the two long strands i-epresent lagging chromosomes. 

 X, 2.- — Egg preserved in 1915 (Gilson's acetic alcohol sublimate). The chromo- 

 somes below those of the inner group on the spindle are in the next section 

 to the remainder. The thick, deeply stained chromosomes of the inner 

 group are probably each two in contact ; it is not certain whether the thin 

 faint lines between them are single chromosomes or spindle-fibres. 

 X, 3-5.— Three stages after the division of the inner group is complete, 

 showing division of the outer group. X, 3 and 5, preserved in 1907 ; X, 4, 

 in 1914. In X, 4, the outer group and all the chromosomes of the inner, 

 except that marked x , are in one section ; the chromosomes of the egg- 

 nucleus (marked $ ) are two sections removed. 



