88 BULLETIN OF THE 
II. Relation of the Observations on Budding in Bryozoa 
to the Germ Layer Theory. 
No question in Bryozoan morphology has been more thoroughly dis- 
cussed than that of the part played by the germ layers in the production 
of the polypide, and upon none has there been less agreement. Nitsche 
first boldly opened the question, and concluded that we have in this pro- 
cess a fatal objection to the idea of the homology of the germ layers, in 
so far as their homology depends upon a similarity of fate throughout the 
Metazoa. A single layer, the invaginated ectoderm, gives rise to the outer 
covering of the tentacles, to the pharynx, and to the brain, — structures 
elsewhere considered as ectodermal, — and also to the lining of the ali- 
mentary tract, elsewhere universally accounted entodermal. In view of 
these facts, “sind die Keimblätter,” concludes Nitsche (75, p- 398), “ kei- 
neswegs mit einer besonderen histologischen Prädisposition ausgestattete 
Zellschichten, sondern lediglich die flächenhaft ausgebreiteten Elemente, 
aus denen die den Metazoenkörper zusammensetzenden, ineinander 
geschachtelten Röhren sich bilden.” Prouho, although recognizing the 
facts to be as stated by Nitsche, has not discussed the theoretical bearing 
of the question. Seeliger (’89", p. 204) finds in the budding process of 
Endoprocta a shortening and confusion of the embryonic process. “ Wie 
die gesammte Knospenentwicklung verkiirzt ist, erscheinen auch die 
beiden Processe der Kinstiilpung durch welche im Embryo zuerst Ento- 
dermkanal, dann Atrium sich bilden, in einen zusammengezogen.” In 
another place (Seeliger, 790, p. 595) the budding process is considered as 
an “immer sich erneuerende Gastrulationsvorgang.” Braem (’90, p. 116) 
regards the inner layer of the bud as entoderm, and the process of its 
formation as one of gastrulation. In a preliminary notice published last 
February (Davenport, 791, p. 279) I suggested that the embryonic tissue 
from which the inner layer of the polypide arises is to be regarded as 
“neither ectoderm nor entoderm, but as still indifferent, and capable of 
giving rise to either.” A few weeks ago I saw for the first time the paper 
of Oka (90), in which he offers (p. 145) a priori a similar suggestion 
concerning the significance of the embryonic tissue from which the inner 
layer of the polypides arises. I am pleased to find that our ideas, thus 
independently arrived at, are so fully in agreement. My idea of the re- 
lation of the germ layers to the layers of the polypide bud chiefly grew 
out of my studies on the embryology of Phylactolsemata as described in 
earlier pages. 
As there are two layers to the bud, the question of the part taken by 
