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. The reason for this is that the
hind part of their body has been drawn up close to the fore part, as
is also the case in the turbinated Testacea. For the Testacea, while
in some points they resemble the Crustacea, in others resemble the
Cephalopoda. Their earthy matter is on the outside, and their fleshy
substance within. So far they are like the Crustacea. But the
general plan of their body is that of the Cephalopoda; and, though
this is true in a certain degree of all the Testacea, it is more
especially true of those turbinated species that have a spiral
shell. Of this general plan, common to the two, we will speak
presently. But let us first consider the case of quadrupeds and of
man, where the arrangement is that of a straight line. Let A at the
upper end of such a line be supposed to represent the mouth, then B
the gullet, and C the stomach, and the intestine to run from this C to
the excremental vent where D is inscribed. Such is the plan in
sanguineous animals; and round this straight line as an axis are
disposed the head and so-called trunk; the remaining parts, such as
the anterior and posterior limbs, having been superadded by nature,
merely to minister to these and for locomotion.
In the Crustacea also and in Insects there is a tendency to a
similar arrangement of the internal parts in a straight line; the
distinction between these groups and the sanguineous animals depending
on differences of the external organs which minister to locomotion
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