1873.] 321 [Morse. 
In the Mollusk, the intestine is always convoluted, not suspended 
freely in the perivisceral cavity, but intimately blended, or united 
with other organs. 
In Vermes there is a peculiar depuratory apparatus characteristic 
of all. In the Annulata this apparatus takes the shape of bilaterally 
symmetrical tubes, in pairs, opening externally and communicating 
with the perivisceral cavity by distinct independent infundibilform 
orifices. (See Fig. 1, s.) 
In the Mollusca, with exception of certain Cephalopoda, nothing 
of the kind is found, and where such communication does exist 
between the organs and the surrounding medium, it is by means of 
simple orifices in the walls of the cavity. 
In the Vermes, especially in the Annulata, a nerve collar is found, 
from which start two parallel chains of ganglia, oftentimes widely 
separated. 
In Mollusks there is also a nerve collar surrounding the esophagus, 
and no double chain, but nerves are thrown out to the sensory, motor, 
and parieto-splanchnic regions. Hence the names Homogangliata, 
and Heterogangliata. In the Annulata, with the exception of the 
Discophora, the generative products are set free in the perivisceral 
cavity, receiving from the fluid therein contained, certain nourish- 
ment. In Mollusks this never occurs, though in certain Cephalo- 
pods the products of the generative organs are set free into a com- 
partment of the perivisceral cavity, and from there find egress through 
the oviduct. 
With the exception of the Octopoda, the pe ig. 2. 
oviduct is single. In the latter group there 
are two oviducts bilaterally symmetrical, 
all of these features being vermian. 
In Vermes the embryo never possesses 
a single or double shell, and with few 
exceptions is distinctly annulated,! while 
among the Mollusks, even when devoid 
of a shell in the adult, the embryo early 
develops a shell composed of one or two 
pieces. 
: : A Embryo of Lamellibran- 
Other differences of minor importance chiate. 
might be mentioned as separating distinct- s, shell; m, mouth; /, 
foot; 6, byssal gland; 
ly the typical worm, from the typical Mol- Gy, (stl 
lusk, but the leading characters here pre- 
1 See “ Norn,’’ p. 10. 
PROCEEDINGS B. S. N. H.— VOL. XV. 21 SEPTEMBER, 1873. 
