No: ti, BODDING IN GOODSTRIA AND PEROPHORA. 205 
as compared with the blood and Ax/age cells, but also as com- 
pared with any other cells whatever of the animal. 
And with almost all the methods of preparation used the 
ectoderm cells stain considerably more deeply, particularly on 
their inner sides, than do the other cells with which we are con- 
cerned. In some instances where the blood cells are particu- 
larly numerous between the ectoderm and the inner vesicle, it 
is wholly impossible to decide whether the “mesenchyme” 
cells are being given off from the inner vesicle or not, so much 
do they resemble the cells of the latter, and so imperfect is the 
separating line between them. But in these cases there is 
not the least possibility of deception about the distinctness of 
the body-space cells from the ectoderm. The difference in 
staining and the clear boundary line, as described above, pre- 
clude it. Now of course, a critical reader, particularly if he be 
inclined to be skeptical, might reply that for a particular 
instance it may be true that the case against the ectoderm is as 
clear as here presented, and that in this instance no cells are 
being given off from it; but that this is very far from proving 
that at some other stage in development, or in some other region 
this process does not take place. I fully appreciate the weight 
of this rejoinder, but in this instance think it wholly over- 
balanced. As to the second part of it, I would say that the 
descriptions and figures all apply to the ectoderm on the dorsal 
side of the bud immediately over the Az/age, or, for stages 
before this has appeared, over the region where it will appear, 
consequently in the region where we should expect the nervous 
system to arise, and the region where, according to Oka and 
Van Beneden et Julin, in Botryllus and Clavelina it does arise. 
It is also the region in which more than elsewhere the char- 
acter of the cells is such that they might most easily be sup- 
posed capable of giving origin to newcells. As already shown, 
the cells are here cuboid in form and have round nuclei and a 
considerable quantity of cell protoplasm. In all other regions, 
on the contrary, the cells are flattened, as are their nuclei also, 
and their protoplasm is relatively less in quantity. The first 
part of the objection is more weighty than the second, but even 
this must, I believe, yield to the facts. We shall allow that it 
