290 
LILIAN SHELDON. 
General Considerations. 
The investigations which I have made on the January 
eggs of Peripatus novse-zealandise, although the stages 
examined were few, nevertheless throw a good deal of light on 
the subject of the early history of the development. In my 
former paper (4) I remarked upon the strange dissimilarity 
which existed from the segmentation stages up to quite late 
ones between the three species of Peripatus whose develop- 
mental history has been at all fully worked at. In the cases 
of P. capensis and P. n ovse-zealandise at all events this 
remark now requires modification. The developmental history 
of the latter is iioav fairly complete as far as the gastrula 
stage, and up to that point its resemblance to that of P. 
capensis is very marked. As I pointed out before (4) the 
segmentation is very similar, the main differences being easily 
accounted for by the presence of the yolk in the one species, 
and its almost total absence in the other. I have now shown 
that in the New Zealand species the ectoderm, which at first 
covers only a portion of the ovum, gradually grows round 
until only a small space on its ventral side remains uncovered, 
and at this spot an invagination takes place forming the 
blastopore, behind which in the middle line the primitive 
streak and groove are present. In all these stages the resem- 
blance to the corresponding ones of P. capensis is very 
striking, the main difference consisting, as in the segmenta- 
tion stages, in the presence of the yolk. This similarity is 
clearly seen on a comparison of the figures in Mr. Sedgwick’s 
paper (1) and my own (4). In fact it seems somewhat strange 
that the almost total loss of the yolk, which must almost cer- 
tainly have been possessed originally by the Cape species, 
should have apparently been accompanied by so few modifica- 
tions in its development, since so important a change of con- 
ditions might have been expected to exert a considerable 
influence on the latter. 
Unfortunately there are many stages wanting between the 
gastrula stage and the next one which I have described in my 
