58 BULLETIN OF THE 
one time; but as he has not attended particularly to this point, this can 
hardly be said to militate against my view. 
There is, however, in my opinion, a more important error in Seeliger’s 
description of the origin of the alimentary tract, — an error into which 
Nitsche (’71, p. 457) also fell. As in Phylactolemata and Paludicella, 
so also in marine Bryozoa in general, so far as I have studied them, the 
posterior and anterior parts of the alimentary tract are formed indepen- 
dently, and their cavities coalesce only secondarily. The constriction 
which separates the lumen of the bud into a cavity nearer, “ vorder,” and 
one more remote from the body wall, “ basal,” does not separate off the 
whole alimentary tract from the atrium. Neither does that constriction 
result in the formation of a space opening into the cavity nearer the 
body wall, “ Vordertheil,” at an upper [distal] point (anus) and lower 
[proximal] point (mouth). Thus if one examines a complete series of 
sections through a polypide even of so late a stage as Figure 92 
(Plate X.), one finds that, while there is an open connection between the 
anal end of the alimentary tract and the atrium, the oral end is at all 
points sharply separated from the cavity above by a double-layered wall 
of cells, as is shown in Figure 92, between œ. and ga. Such a condition, 
moreover, has been found by Barrois (’86, pp. 73-76) in the primary 
polypide of Lepralia, and by Prouho, as just stated, in the primary 
polypide of Flustrella. 
Origin and Development of the Ring Canal and Tentacles. — Nitsche 
(71, p. 430) first described in Flustra a ring canal surrounding the 
mouth-opening and lying at the base of the tentacles, but did not refer 
to the origin of it. Seeliger (90, p. 588) describes it in a young pol- 
ypide of Bugula, as derived from the mesodermal layer. 
My own sections also show that it arises on each side of the cesopha- 
gus as a groove lined by mesoderm (Plate X. Fig. 92, right). This 
canal, which is shown cut along its course in Plate IX. Fig. 82, can. 
cre., is not wholly separated from the body cavity, but communicates 
with it below the brain. This communication occurs in the section 
below that shown in Figure 82, near the point can. erc. This ring 
canal at an earlier stage is shown in Figure 87. It has not yet been 
formed backwards nearly so far as the brain; anteriorly the section has 
traversed the tentacles under which it runs. The canal is also shown 
cut across in Figure 86 at the base of a tentacle, with whose lumen its 
cavity is directly continuous. 
The formation of the tentacles is closely connected with that of the 
ring canal, from the upper wall of which they arise. Since the upper 
