EARLY STAGES OF SEGMENTATION OF ECHINUS HYBRIDS. 487 
nsaally found. In pure esculentus the process of conjuga- 
tion appears to be more like Avhat v/e have found, in the 
esculentus c? hybrids. The zygote nucleus swells, irregular 
masses of chromatin appear within it, and. become concen- 
trated. into small elongated, chromosomes, the number of 
which is about thirty-eight. As the nuclear membrane dis- 
appears, and the spindle is completely formed, the chromo- 
somes, at this stage scattered irregularly, become shortened 
and thickened, and often clumped in pairs or groups, so that 
a count usually gives a number much lower than that at 
rather earlier or later stages. Sometimes, however, they are 
scattered more separately, so that each can be seen distinctly, 
and here again thirty-eight may be counted (fig. G, a, 1). At 
about this stage, however, the abnormal featui'e of the mitosis 
appears; small vesicles of varying size and number appear 
among the chromosomes, distributed irregularly on the 
spindle (figs. 7-11). In eggs preserved with osmic fixatives 
these vesicles are faintly and evenly stained, except that 
the edge is more deeply stained than the centre ; iu 
sublimate preparations they have more the form of minute 
nuclei with small stained dots under their enclosing mem- 
brane, and are rather similar to the vesicles normally formed 
by the chromosomes in the late anaphase as they cluster 
round the pole of the spindle, although quite distinct from 
them. 
A comparison of a series of prophase figures, or even of the 
vesicles in one figure, leaves no doubt that thej’ are formed from 
chromosomes, for all stages may be found between a chromo- 
some which appears somewhat swollen and a fully formed 
vesicle (figs. 7, 8, a-z). Hut it is also quite clear that iu 
many cases the whole chromosome is not used up in forming 
the vesicle ; often apparently normal chromosomes may be 
seen to which a vesicle is attached, either at its side or atone 
end. The number of vesicles which are formed at this stage 
varies from one or two up to about six or seven, or occasion- 
ally even as many as twelve, as shown iu the counts in 
Table I. 'I'he considerable variation in the number of chromo- 
