In opposition to its interpretation as a segment of the body,
only the want of limbs can be cited; in its favour we have the relation
of the intestine, which usually opens in this piece, and sometimes even
traverses its whole length, as in Microdeutopus and some other
Amphipoda. In Microdeutopus, as Spence Bate has already pointed out, one
is even led to regard small processes of this tubular caudal piece as
rudimentary members. Bell also ('British Stalk-eyed Crustacea' page 20),
states that he observed limbs of the last segment in Palaemon serratus
in the form of small moveable points.
The attempt has often been made to divide the body of the higher
Crustacea into small sections composed of equal numbers of segments,
these sections consisting of 3, 5 or 7 segments. None of these attempts
has ever met with general acceptance; my own investigations lead me to a
conception which nearly approaches Van Beneden's. I assume four sections
of 5 segments each--the primitive body, the fore-body, the hind-body,
and the middle-body. The primitive body includes the segments which the
naupliiform larva brings with it out of the egg; it is afterwards
divided, by the younger sections which become developed in its middle,
into the head and tail. To this primitive body belong the two pairs of
antennae, the mandibles and the caudal feet ("posterior pair of
pleopoda," Sp.
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