232 
KICHARD ASSHETON. 
the whole yolk and hypoblast mass, so that the large inner 
cell, called by Selenka hypoblast, corresponds to the lower 
ring of Hill’s description and has slipped inside the upper 
ring, resulting in a condition not unlike the Monotremes 
(vide diagram A in the above text-figure). 
I should like to take this opportunity of collecting an error 
in a drawing on p. 681 of O. Hertwig’s ' Handbuch,’ vol. i. 
Fig, 244 is said, by Professor Richard Hertwig, to be 
“ Furchungsstadien des Schafes nach Assheton,” and in it 
two figures are given of what appears to be the four-cell 
stage of the sheep. The drawings are really those of the 
rabbit, not sheep, and are taken from my ’94 paper on the 
“ Re-investigation into the Early Stages of the Development 
of the Rabbit.” 
The second figure shows the four-celled stage with the 
segments arranged in the way I have just taken to be typical 
for Metatheria. I have no recollection of the specimen now, 
so cannot say whether the manipulation can have in any way 
accounted for the abnormal displacement — if abnormal it is, 
as I believe. 
Anyhow, it is the only figure I have been able to find after 
searching Rischoff, Coste, van Beneden, Duval, Selenka, 
Sobotta, Heape, Melissinos, etc., who have observed specimens 
of Eutherian four-segment stages in which the segments 
are arranged thus. 
A possible — and indeed probable — explanation is that this 
specimen was obtained immediately after division, at which 
time it is possible that they may lie in one plane, the twisting 
being due to some cytotropic influence which places the two 
pairs almost immediately in the crossways position, where 
they remain for the next two or three hours till the third 
cleavage plane arises. It is clear that whereas it may very 
rarely happen that the stage immediately succeeding the 
second division is obtained if it last but a few minutes, the 
foui’-celled stage in the crossways position lasting two to three 
hours will turn up much more frequently. Of recent years 
1 have seen four-segment stages of rabbit, pig, dog, ferret. 
