Medical Officers of the Army of India.

63

and when, on my closer approach, it endeavoured to go further in, there was
evoked from the rightful tenant in the depths an angry whirr of remonstrance.
Thereafter I was often able to elicit the sound by catching an individual and forc-
ing it into a strange burrow: the captive was always most unwilling to enter,
but if he were forced in, the rightful owner would very soon let him know, by a
vigorous chiding from the stridulating organ, that he was not wanted.

       In this deeply burrowing species one use of the stridulating apparatus thus
appears to be to warn away trespassers and obviate the risk of suffocation; for
if a lot of crabs were to crowd into one burrow they would all, probably, be
stifled.

        In Ocypoaa ceratophthalma, which does not burrow deeply, this cannot be
the use of the organ. Captain A. R. S. Anderson, who heard this species
croaking like frogs, on one of the Laccadive Islands, says that the noise was
being made without any apparent cause.

       I may mention that my predecessor here, the late Prof. J. Wood-Mason, who
first called my attention to the musical powers of the Crustacea, discovered
what, though their function has not been verified, are probably strepitant organs,
in a small species of Peneus closely related to Peneus velutinus, in a species
of Squilla which he named S. stridulans, and in a species of Carcinoplacoid
crab to which he gave the significant name Psopheticus stridulans.

       Moreover there are several species of Hermit-crabs, some of which are re-
ferred to in the literature, while others are not, in which organs that can only be
useful for crepitation exist.

       Finally I may refer to the Catometope crabs of the genera Macrophthalmus
and Metaplax, the " musical organs " of which have been described by de Man.
Here the sound, as in the majority of stridulating insects, seems to have a sexual
meaning, since the organ that makes it is found only in the male. Perhaps some
" Investigator " Naturalist may have an opportunity of noting what the sound is
like, and in what circumstances it is heard, for these crabs are common enough in
the creeks of Indian deltas.

2.—Sounds made by Fishes.

       The literature on this subject is very considerable and dates from the time of
Aristotle, and a large number of fishes are now known to be able to utter sounds
that are more or less musical, quite distinct from the meaningless gaspings of a
fish when taken out of water.

       Apart from the irregular sounds caused by spasmodic movements of the lips,
jaws, gill-covers, fin-rays, etc., sounds expressive of emotion of some sort are
caused, or are supposed to be caused, (1) by grinding together of the pharyngeal

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