Geology and Natural History. 155 
either in the number and form of the jaws (Diopatra, ete.), or in 
the cephalic appendages, as in Serpulidew, where one of the 
branchi 
ventral regions are often quite as strongly contrasted as in any 
mollusk; and in some cases the body is compressed laterally 
on 
18 a very poor character for characterizing any large group o 
animals, and should have little or no weight in this case. The 
tral connections of the “locomotor muscles” in mollusks and 
their lateral and dorsal attachment to the integument in wort 
are given as distinctive. But we generally find the locomotor 
muscles of animals connected with the locomotive organs, w er- 
ever these may be situated. So in Pecten we find that the main 
locomotor muscles are attached laterally to the shell, that being 
its principal organ of locomotion; and in Cephalopods we find 
them on the sides and back, as well as ventrally, so that the man- 
tle may be used as a locomotive organ. On the other hand, many 
worms, like Aphrodite, Lepidonotus, many leeches, Trematodes, 
and other worms, both high and low, have their locomotive organs 
as truly ventral as those of Gastropods. “In the Mollusk the 
forming a sac or mantle, inclosing a conspicuous cavity, and pro- 
tecting the gills.” This is, indeed, a valuable character, but not 
1s often nearly or quite abortive, and the gills are often situ- 
ated on the back or sides, as in the Nudibranchs. But in this 
character the Brachiopods agree with the Mollusks, and not with 
“In the worm the digestive canal is straight, rarely 
convoluted, and suspended freely in the perivisceral cavity.” “In 
the Mollusk, the intestine is always convoluted, not suspended 
freely in the perivisceral cavity, but intimately blended, or united 
ns.” e intestine varies immensely in bot 
very long and greatly convoluted, and may terminate either ante- 
"orly or posteriorly. 
, +2 most Nemerteans, Planarians, and Trematode worms the 
intestine is not “freely suspended,” but firmly united to the other 
°rgans and the tegumentary system. “In Vermes a 
peculiar depuratory apparatus characteristic of all. : 
lata this apparatus takes the shape of bilaterally symmetrical 
tubes, in pairs, opening external 
