340 bulletin: museum of comparative zoology. 



pairing process during the prophase. When the spindle is seen sidewise 

 (Fig. 118) the chromosomes appear as small circular masses ; and the 

 spindle as a whole is comparatively broad and short. As a rule, the 

 splitting takes place in all chromosomes before the migration to the pole 

 commences, and this migration being nearly simultaneous, daughter 

 plates are formed (Fig. 119). But unfortunately I have not been able 

 to count the number of the chromosomes in any of these. During the 

 migration the chromosomes usually preserve their original orientation 

 (Fig. 119), but occasionally they turn so as to lie with their long axes 

 nearly parallel with the spindle fibres. The later anaphase and the telo- 

 phase present no features of special importance. The chromosomes, as 

 they approach the poles, become closely crowded together, though never 

 completely fused, and when they once more separate are seen to be con- 

 nected together in an irregular network, perhaps through confluence at 

 their previous points of contact, just as takes place in other cell genera- 

 tions. With the migration of the daughter chromosomes interzonal 

 filaments are formed, which, as is usual in this animal, are much stouter 

 and of more clearly fibrous nature than the spindle fibres. At the end 

 of the anaphase the latter break down ; the centrosornes disappear — 

 though they may of course persist undetected — and with the constric- 

 tion of the cell the interzonal bridge also disappears, so that the two 

 daughter cells become entirely separate, instead of remaining connected, 

 as so commonly occurs in the maturation divisions of the male germ 

 cells. This mitosis presents, as such, no especial points of interest, ex- 

 cept for the very striking resemblance of its metaphase and anaphase to 

 those of the spermatogonia, and the corresponding difference from the 

 entoderm cells (compare Figs. 116, 118, 119, with Figs. 30, 31, 32). 

 The feature important to be borne in mind is that all the mitoses occur- 

 ring in the female gonad are certainly of this one type, and, as certainly, 

 all belong to the same cell generation, the obfronia. It was chieflv to 

 establish definitely whether or not this was the case that I followed 

 through the mitotic changes in detail. 



At the close of the oogouial mitosis the nucleus, after a brief telo- 

 phase, in which the nuclear membrane re-forms and its contents arrange 

 themselves in a loose net, passes into the so-called "resting" condition, 

 as is the case after all the other cell divisions studied. The nucleolus 

 reappears ; the nuclear space becomes filled with dense karyoplasm, and 

 the chromosomes entirely break down and pass into the diffuse condition 

 so commonly described. 



It is thus certain that in Gonionemus after the last oogonial division 



