MUSEUM OF COMPARATIVE ZOOLOGY. 95 
to Braem’s (90, Taf. VII. Fig. 89 mb.) observations, which I can abun- 
dantly confirm, — and to the coelomic epithelium of the adult stock, In 
the few series of sections of the proper stage which I possess, I have not 
found with certainty the degenerating cells of which Korotneff speaks ; 
but even if they regularly occur, I should be inclined to regard them as 
the degenerated entoderm, the mesoderm persisting to give rise to the 
muscular tissue and the ccolomie epithelium. 
From a consideration of these facts, — that the larvee are homol- 
ogous and the process of gastrulation is comparable throughout the 
Ectoprocta, that in the least modified larvae both functional entoderm 
and mesoderm are produced by that gastrulation, that one of these 
two germ layers has become rudimentary in Phylactoleemata, that 
it is highly probable that the entoderm has disappeared from loss of 
function, and that the layer which persists gives rise to the muscula- 
ture, sexual cells, and coelomic epithelium, — I conclude that the inner 
layer of the Phylactolematous larva, and therefore the outer layer of the 
bud, is mesoderm, 
If we accept the point of view of Kleinenberg (86, pp. 1-19) and ad- 
mit the existence in general of only two layers, ectoderm and entoderm, 
a clearer conception of the modification undergone by the Phylactolema- 
tous larva may be gained. We may divide the entoderm arising in 
Bryozoa into two parts; viz. (1) that which gives rise to the lining 
of the midgut, as in Cyphonautes, and (2) all the rest of the inner 
layer. Now, since no midgut is formed in the Phylactoleematous larva, 
part (1) of the entoderm has ceased to be differentiated ; all which 
remains, then, is part (2); but this is equivalent to “ mesoderm” in 
the sense in which I have employed it, and therefore T am justified 
in saying that “mesoderm” only is produced. 
The question has now to be answered, What is the significance of the 
inner layer of the bud? Two different answers have been given to this ques- 
tion. It has been maintained, on the one hand, that it is to be regarded 
as ectoderm; on the other, as entoderm. There are serious difficulties 
in the way of accepting the first view, — so serious, in fact, that few 
authors have maintained it, although at first glance it seems to be re- 
quired by the facts. Although we have not yet sufficient grounds for 
declaring that organs formed by budding. must be built up from the 
same germ layers as corresponding larval ones, —although we may ad- 
mit that gemmigenesis recapitulates phylogeny and corresponds with 
ontogeny only in an imperfect and confused way, — still, from the expe- 
rience gained by tracing the development of hundreds of animals from 
