96 BULLETIN OF THE 
the most widely separated groups of the animal kingdom, the idea that 
a functional alimentary tract is ever wholly derived from differentiated 
ectoderm will not be accepted by most embryologists without conclusive 
evidence. 
The second view is that the formation of the inner layer of the bud 
is a process of gastrulation, giving rise to entoderm, and that the so- 
called “ gastrulation ” of the sexual ontogeny of Phylactolaemata is to be 
regarded as a precocious ingression of mesoderm only. 
Two considerations are opposed to this view. In Membranipora there 
is a gastrulation which gives rise to the entoderm and mesoderm of the 
larva; and since the gastrulation of Phylactolemata is similar, these 
clements must be potentially present here also. The “gastrulation” 
in Bryozoa is a normal one; if there is any entoderm in the body wall 
giving rise to the inner layer of the bud, it must have been ento- 
derm which failed to become invaginated. But what, in the second 
place, is to be gained by assuming that the inner layer of the bud is 
formed from entoderm? Here is as great a difficulty as before, since the 
nervous system originates from this layer. It has been maintained in 
many cases that the nervous system arises from mesoderm, and Seeliger 
(89, p. 602) believes that it is formed from that layer in the non-sexual 
reproduction of some Tunicates; but I know of no good evidence of its 
origin in any of the Triploblastica from entoderm. 
Before going on to state my conception of the significance of the 
inner polypide layer, I desire to call attention to the conditions in the 
region at which it is first formed. I have shown above (page 69) that 
the primary polypide or polypides arise from the pole of ingression in 
Phylactolemata, and that therefore in this group the aboral pole (in the 
sense of Barrois) corresponds to the pole of ingression. As I under- 
stand Barrois, he means by oral pole merely the pole which in Cypho- 
nautes, for instance, bears the nõouth, — the pole also by which the 
larva attaches itself. Braem (90, p. 123, foot-note), however, interprets 
“oral side” in Barrois’s sense to mean in the last instance the place at 
which gastrulation takes place. Perhaps Barrois does somewhere state 
such to be the significance of his term (I have not found the place), 
but in that case I can only say that, to my mind, he has not produced 
sufficient evidence to prove that the oral pole of the larva of Gymno- 
læmata is the same as the pole of ingression in the gastrula ; nor, in my 
opinion, has any other investigator done so. Nearly all species studied 
have a stage early in their development when their poles are very sim- 
ilar, and orientation certainly would be exceedingly difficult. One of the 
