304 
THE OCEAN WORLD. 
ct 
the 
junction of the haemal with the neural region, the Ep, 'podium ('' Ji’)‘ 
The mass of the body between the foot proper and the part of 
abdomen which bears the epipodium may be termed the mid-body’ 
or Mesosoma. On the upper part of the sides of the head are t ff0 
pairs of organs, namely, the eyes and tentacles. In the hasmal reg 1011 
the integument may be modified and raised up into a fold at the edg eS > 
either in front or behind the anus. When so modified, it is called 9 
mantle, Pallium. In front of the anus again, the branchim ( t ) pr°J e ' 
as processes of the haemal region. Among the internal organs, 
heart ( u v) lies in front of the branchiae in the haemal regions, t ' 11 
nervous ganglia (x y z), of which there are three principal pairs, beu>r 
arranged around the elementary canal which they encircle.” 
Such is the general type of the class Mollusca, of which, howe ver ’ 
the variations are innumerable. They are all soft-skinned ani® 9 ^’ 
without either articulated exterior or annular external skeleton. Th el * 
nervous system, being without cerebro-spinal axis, is entirely comp° se 
of ganglions, which arc all reunited in the oesophagus without con 8 * 1 
tuting in any case a lengthened median chain. Their digestive org 9 ®* 
are complete — that is, they are provided with two apertures; tb el 
principal organs are symmetrical and according to a plan, usual!? 
curving, by which their bodies are divided into two parts. ^ 
Our limits forbid us to dwell upon the organization, manners, aIlt 
distribution of these soft flimsy creatures : our object will be to ® 9 
known, as they come before us, the more curious and import 9 
species, following a scientific order conformable to the divisions est® 
blished by the best modern naturalists. 
Molluscs vary so singularly among themselves, that it is difficult 0 
establish unity in their littlo world. We propose dividing them i nt " 
two principal series, the first of which establishes in some sort t^ e 
passage between the zoophytes, whose history we have just conclude > 
and the mollusc, properly so called. This first series or subdivision 
to which Milne Edwards has given the name of Molluscoida, include® 
under that term the Bryozoaires, Ascidians, and Tunicata. 
The Molluscs, properly so called, are grouped into four clas^ e ® 
I. Acephalous Molluscs. II. Gasteropodous Molluscs. Ill- W et ° 
podous Molluscs. IV. Cephalopodous Molluscs. 
