Affinity of Mollusca and Molluscoida. By W. K Broohs. 143 
that the Polyzoa are fixed ; in fact, those which are developed from 
statoblasts are at first free, and swim by means of the cilia of the 
lophophore. 
The similarity between the Polyzoa and true Mollusca, in 
general plan of structure, has long been recognized, but the at- 
tempts to connect the two groups through the Lamellibranchs are 
so evidently incorrect, that, led by the unquestionable afiinity of the 
Polyzoa and Brachiopods to the Vermes, many geologists are now 
inclined to separate these lower forms from the Mollusca proper. 
As soon as we recognize that the Lamellibranchs are not to be 
regarded as typical Mollusca, and that all of the latter are to be 
traced back to a " Veliger," all difficulty seems to disappear, and it 
becomes plain, not only that the Mollusca and Molluscoida are 
related, but that they are connected so closely, that the advisability 
of such a division is very doubtful. We also obtain, at the same 
time, an explanation of the worm-like early stages of the embryo, 
exhibited by so many of the true Mollusca. The belief so firmly 
supported by nearly all zoologists a few years since, that the various 
branches of the animal kingdom are absolutely independent of each 
other, has been almost entirely overthrown by the accumulation of 
new facts, and the constantly increasing tendency to examine them 
in their bearing upon the theory of the evolution of life ; and the 
union or junction of the Vermes and the Mollusca, in some manner, 
has already found a number of advocates. 
Professor Morse, by his investigations upon the anatomy and 
embryology of the Brachiopods, has shown that, if we consider this 
group by itself, it must be placed with the Annelids. His investi- 
gations also show, with equal clearness, that the Brachiopoda are 
closely related to the Polyzoa, and we must therefore regard them 
as united by the Veliger " to the true Mollusca. If we accept the 
view that the moUuscan and vermian stems are thus united, the 
question, " Are the Brachiopods Worms or Mollusks ? " will be 
regarded as nothing but a verbal discussion ; for this class forms the 
connecting link between the two groups, and any sharp line of 
demarcation does not exist. 
We are now prepared to form a provisional phylogeny of the 
Mollusca, which may be stated as follows : 
The Brachiopods are derived from the Vermes ; and from the 
Brachiopod stem, but from something very difi'erent from any known 
Brachiopod, the Polyzoa originated. From the Polyzoon stem, but 
not from any known Polyzoon, we have the Veliger. The true mol- 
lusks have originated as several ofi'shoots from this Veliger stem. Of 
these the Scaphopods seem to be the least speciahzed, and in most 
respects nearest to the original proto-mollusk. The Pteropods are 
the representatives of another ofishoot, to which the Cephalopods 
also seem to belong. The Gasteropods seem to represent several 
