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. The position of the mytis shows that it
corresponds to the heart of sanguineous animals; for it occupies the
self-same place. The same is shown by the sweetness of its fluid,
which has the character of concocted matter and resembles blood.
In the Testacea the presiding seat of sensation is in a
corresponding position, but is less easily made out. It should,
however, always be looked for in some midway position; namely, in such
Testacea as are stationary, midway between the part by which food is
taken in and the channel through which either the excrement or the
spermatic fluid is voided, and, in those species which are capable
of locomotion, invariably midway between the right and left sides.
In Insects this organ, which is the seat of sensation, lies, as
was stated in the first treatise, between the head and the cavity
which contains the stomach. In most of them it consists of a single
part; but in others, for instance in such as have long bodies and
resemble the Juli (Millipedes), it is made up of several parts, so
that such insects continue to live after they have been cut in pieces.
For the aim of nature is to give to each animal only one such dominant
part; and when she is unable to carry out this intention she causes
the parts, though potentially many, to work together actually as
one. This is much more clearly marked in some insects than in others.
The parts concerned in nutrition are not alike in all insects, but
show considerable diversity
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