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of chromatin substance in the nuclei, which makes it very trouble- 
some to obtain a satisfactory staining of the sections. To this must 
be added the difficulty in orientating the embryos by the sectioning; 
while no orientation at all is possible on embryos still lying within 
the egg membrane, it is possible, of course, to arrange the sections 
of the free embryos in transverse or longitudinal direction, but it 
is only after the formation of the vestibulary invagination that it 
is possible to direct the longitudinal sections in the sagittal or 
frontal plane. Considering furthermore the tendency of the larvæ 
in the aquaria-cultures to grow abnormal, there is only too much 
reason for the incompleteness of the record of the developmental 
processes of this larva. 
As soon as the blastula is formed, after about 6 hours, the 
formation of the mesenchyme begins, and the blastocoel cavity is 
soon filled with a dense mass of mesenchyme cells. The gastrula 
invagination does not occur till a much later stage, about the 
time when the embryo is about to leave the egg membrane, and 
the blastopore — which is very small — does not close until 
the embryo has become free. The invaginated portion is not a 
simple sac, but, while still remaining in open connection with the 
exterior, is flattened in the longitudinal axis. The later subdivisions 
of the invaginated portion I have been unable to trace with cert- 
ainty; I would only say that it is intentionally that I do not call 
the invaginated portion the archenteron, because I am not at all 
sure that the stomach derives from this part. In faet, there are 
indications of more than one invagination taking place, in which 
case probably the enterocoel vesicles alone develop from the in¬ 
vagination mentioned. The enterocoel vesicles do not shift their 
position in quite the same way as in Antedon mediterranea — 
and the other Crinoids thus far studied (see the authors memoir 
quoted above) —; at the time when the vestibulary invagination 
is forming, the two vesicles are still lying in their original position, 
on the right and left side of the embryo, the mesentery between 
them being in the posterior midline. Regarding the formation of 
the hydrocoel, parietal canal etc. I do not venture to put forth 
any statements. 
It is evident already from the few facts recorded here that the 
development of this species differs so markedly from its supposed 
