_Neoceratodus_ a grunting noise which may be heard at night for some distance. Whatever the nature of the vocal mechanism, it is highly probable that the sounds produced by Fishes travel to considerable distances in the water, inasmuch as the latter medium is a far better conductor of sound than air, and, moreover, the transmission of sound-vibrations from the air-bladder to the water is facilitated in many Fishes by the fact that, for a portion of its extent on each side the bladder is in direct contact with the superficial skin behind the pectoral girdle. From the by no means exhaustive list of examples given above, it is obvious that in some form or other vocal organs are present in a considerable number of Fishes, both freshwater and marine, belonging to widely different groups; and further, that even in the same species (e.g. _Doras maculatus_ and other Siluridae), both stridulation and the action of extrinsic muscles on the air-bladder may be utilised as a means of sound-production. Certain Teleostean families like the Siluridae, the Sciaenidae, and the Triglidae, seem to be distinguished above all others by the {364}prevalence of some form of vocal organ. According to Sörensen, the first mentioned of the three families includes no less than 68 species, which utilise the air-bladder alone as a sound-producing organ. Nevertheless, there still remain many Teleostean families, rich in genera and species, and with an almost world-wide geographical distribution, in which such organs have not yet been found. The advantages which Fishes derive from the possession of sound-producing organs are sufficiently obvious.