154 SUPPLEMENT 
say, that this branch of zoology has been much indebted to 
the subsequent labours of the French naturalists we have 
already cited, and to others of the same nation; to some 
zealous philosophers of Germany, such as Oken and Dr. 
Goldfuss; to some of the United States of America, as Mr. 
Say; and last, though not least, to some distinguished men 
amongst ourselves, of whom we shall merely mention Dr. 
Leach and Mr. Gray. To enter into an analysis of their 
systems and improvements would be wholly beside our pre- 
sent purpose. 
We shall now briefly treat first of the form and organization 
of the animals of this class. 
The form of the body of the molluscous animals is extremely 
variable, though it presents the constant negative character 
of being never articulated. ‘Thus, though most usually oval, 
more or less elongated, convex above, plane underneath, as in 
doris, limax, &c., yet it is sometimes equally oval and con- 
vex, above and underneath, as in sepia, elongated and sub- 
cylindrical, as in certain loligines, globular, as in octopus, it 
is often compressed more or less strongly on the sides, as in 
scyllea, and particularly in all the lamellibranch acephala. 
It may also be very much elongated and claviform, as in the 
teredo and neighbouring genera. In many cephala a large 
portion of the body is rolled, like the shell, into a spiral more 
or less elevated, and of different forms. Ia fine, the form may 
be so irregular that the animal scarcely appears symmetrical 
externally, as is the case with the ascidiz and neighbouring 
genera, and even in the biphore. 
A tolerable number of these animals presents a very clear 
separation between the head and the rest of the body, as in 
octopus. Sometimes, however, it is much less marked, as in 
doris, &c.; and finally, in an entire class, consequently named 
acephalous, this separation no longer takes place, and no head 
properly so called exists. 
a te —— 
