FORMATION OF GERM-LAYERS IN CRANGON VULGARIS. 361 
of the later development, and a fuller description of the embryo 
at this stage is therefore deferred. 
The agreement between the account here given of the 
formation of the layers in Crangon, and that given by 
Nusbaum of the corresponding process in Mysis, is on the 
whole fairly complete; but there are, nevertheless, certain 
points of difference which are not unimportant. The cells 
which are here spoken of as anterior endoderm correspond 
closely in their mode of origin with Nusbaum’s “ Vitellophags,” 
being cells which separate from the rest of the blastoderm 
before the main body of the endoderm, and which immediately 
wander through the yolk. The corresponding cells of Mysis 
differ from those seen by me in the fact that they are separated 
from the superficial portions of the blastoderm at a slightly 
earlier stage; but they resemble the cells of Crangon in arising 
from the blastoporic area, which serves in both cases as a 
centre of dispersion, from which the cells scatter through the 
yolk. The statement repeatedly made by Nusbaum that these 
cells take no part in the formation of the alimentary epithe- 
lium does not seem to me to be proved either by his descrip- 
tions or by his figures. The extreme rarity of the “ Vitello- 
phags”’ in all those stages in which an endodermic epithelium 
occurs makes an interpretation of Nusbaum’s figures, similar 
to that which is here offered in the case of Crangon, seem 
perfectly possible. The formation of a tubular endodermal 
tract, open in front towards the yolk, and early connected with 
a ventral anterior sheet of endoderm is a point in which the 
the two genera closely agree. 
The formation of the mesoderm from two ventral ectodermal 
plates is also described by Nusbaum. In Mysis, however, 
these plates appear to extend further forwards than in the 
shrimp, and a formation of a zone of large budding cells does 
not occur. 
The many points of difference between Professor Kingsley 
and myself have been already alluded to, and I can only 
express regret for their existence, without being able in any 
