34 BULLETIN OF THE 
One cannot refrain from noticing the similarity in the relations of the 
“under lip” of Rotifers (Zelinka, ’91, Taf. III. Fig. 55) and the epistome 
of Bryozoa (cf. also the foot of Mollusks). 
Zelinka has also shown (p. 397) that in Callidina at an early stage 
two lateral folds appear on the ventral side of the embryo, enclosing be- 
tween them the mouth and under lip. These folds extend along about 
one half of the length of the embryo. Later they become relatively 
shorter, and finally form the lobes of the wheel organ. They have also 
precisely the position of the lophophoric ridges of Ectoprocta at an early 
stage, as I have figured it (’91, Fig. 25), lying on each side of the mouth 
and ganglion. They have also the same relations as the ridges from which 
the gill filaments arise in Lamellibranchs. Lankester’s (’74, p. 80) view 
of the homology of the tentacles of Bryozoa and gill filaments of Lamelli- 
branchs is thus strengthened. 
Finally, there is between Rotifers and Endoprocta a striking similarity 
in the position of anus and urogenital ducts, which in Urnatella, as in 
Rotifers, open into a common cloaca on the suba@sophageal aspect be- 
tween mouth and anus. Such a resemblance is especially striking in 
footless genera like Asplanchna (which, however, has no anus, cf. Ma- 
sius, 791, fig. 1) and Hertwigia (L. Plate, ’85, Fig. 7), —genera resembling 
more nearly the ancestral form, since the foot, lying behind the anus, 
must be considered as a secondarily produced appendage. 
To sum up: The embryological as well as the anatomical evidence 
seems to sustain the view that Bryozoa are closely related to Rotifers, 
the two groups having sprung from an ancestor which was common to 
them and Mollusks also ; that after the Rotifer stem had branched off, 
the common Mollusco-Bryozoan stem produced tentacles on the lateral 
ridges ; that the two groups then soon separated, the Mollusca to un- 
dergo an extensive and complicated development, the Bryozoa to remain 
at a low level. The chief changes which the Bryozoa have experienced 
are (1) the acquiring of a body-cavity through the relative decrease in 
amount of the mesenchyme, that which remains forming an epithelium 
(Phylactolemata); (2) the loss (?) of the protonephridia and sexual 
ducts in Ectoprocta; (3) the loss of the epistome (Gymnolemata) ; 
(4) the loss of the preoral ganglion; (5) the acquiring of 2 ccecum (Ec- 
toprocta); (6) the multiplication of methods of reproduction, by regen- 
eration, by budding (without and with stock-formation), by division of 
stocks, and by statoblasts. 
CAMBRIDGE, September 27, 1892. 
