ACCOUSTIC AND HYDROSTATIC USES OP. . xlv 



tubes coalesce previous to entering the dorsal wall, of the alimentary canal. 

 Not only in the Cyprinidce but also in the Gharacimdce and Siluridce a 

 chain of auditory ossicles connects the air-bladder with the internal ear, 

 instead of a tube filled with gas, as remarked upon in .the Physoclisti. 

 Three ossicles on either "side pass forwards along the under surface of the 

 body of the first vertebra, connecting the outer wall of the air-bladder with 

 the atria of the vestibule. These 'ossicles were first pointed out by Weber; 

 and since his time it has been shown that they belong, like the capsules of 

 the special organs of sense, to the splanchnoskeleton. 



In tbe same family, or that of carps, we find a curious form of 

 loach, Botia, in the East Indies, that can scarcely be said' to be 

 entirely a ground-feeder, but seems intermediate in habits between the true 

 carps and the grovelling loaches. It. has the anterior portion of its air- 

 bladder, or what may be termed the acoustic part, more or less enclosed in 

 bone, this being formed from 'the parapophyses of some of the anterior 

 cervical vertebras. All fish with the air-vessel enclosed in bone are bottom' 

 feeders, and very few are destitute of barbels. In the true ground-feeding 

 loaches, as the Nemacheilus and Gobitis, it almost appears as if the posterior 

 two-thirds of the air-bladder, or its hydrostatic portion, were deficient ; the 

 organ being in the form 'of two round lobes, placed side by side, below the 

 bodies of some of the anterior vertebras, where they are almost entirely 

 enclosed in bone. The pneumatic tube, however, is still found to exist. In 

 another exclusively ground-feeding form of carp, Homaloptera, in the East 

 Indies, and in which the lower surface of its body appears fiat, and its 

 general conformation refers to its habit of clinging close to stones at the 

 bottom of streams, we find the air-bladder entirely wanting. 



Another fresh-water family of Physostomi, the Oharacinidce, residents 

 of tropical Africa and America, are exceedingly interesting, as regards how. 

 this organ is modified in respect to hearing;, a chain of auditory ossicles 

 extending from it to the internal ear, as observed in the Cyprinidaa'. While 

 in Hri/tJtrinus we perceive a most interesting link between the Physostomous 

 Teleosteans on one ' hand and the ai'r-breathing Ganoids on the other, for 

 in this genus, although the air-bladder is above the alimentary canal, the 

 pneumatic tube pierces the left, side of the throat. The air-bladder is 

 likewise sub-divided by fibrous partitions, but whether -such are exceedingly 

 vascular or not, whether this organ is used for respiration or simply for 

 flotation, there does not appear at present to be evidence upon which to 

 decide. • . # ' 



The extensive fresh- water Physostomous family (which has likewise 

 so/me marine representatives) of Siluridce, or sheat-fishes, is very abundant 

 .in the tropics. Among them the air-bladder is remarkably modified, in the 

 majority of instances being apparently more useful for auditory that for 



