the rest. In this form the feet remain for a very long time, whilst the
abdominal appendages grow into powerful natatory organs, and the eyes,
which at first seemed to me to be wanting, into large hemispheres. In
the transition to the form of the adult animal the last three pairs of
feet (Figure 49) especially undergo a considerable change. The
difference between the two sexes is considerable; the females are
distinguished by a very broad thorax, and the males (Lestrigonus) by
very long antennae, of which the anterior bear an unusual abundance of
olfactory filaments.

Their youngest larvae of course cannot swim; they are helpless little
animals which firmly cling especially to the swimming laminae of their
host; the adult Hyperiae, which are not unfrequently met with free in
the sea, are, as is well known, the most admirable swimmers in their
order. ("Il nage avec une rapidite extreme," says Van Beneden of H.
Latreillii M.-Edw.)

The transformation of the Hyperiae is evidently to be regarded as
ACQUIRED and not INHERITED, that is to say the late appearance of the
abdominal appendages and the peculiar structure of the feet in the young
are not to be brought into unison with the historical development of the
Amphipoda, but to be placed to the account of the parasitic mode of life
of the young.

As in Brachyscelus, free locomotion has been continued to the adult and
not to the young, contrary to the usual method among parasites. Still
more remarkable is a similar circumstance in Caligus, among the
parasitic Copepoda. The young animal, described by Burmeister as a
peculiar genus, Chalimus, lies at anchor upon a fish by means of a cable
springing from its forehead, and having its extremity firmly seated in