ACCOTJSTIO AND HYDROSTATIC USES OF. xlv 



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

 Not only in the Oyprinidm but also in the Gharadnidui 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 Physocliati. 

 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 the 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 vertebrae. 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 Cdbitis, 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 groundrfeeding form of carp, Homaloptera, in the Bast 

 Indies, and in which the lower surface of its body appears flat, 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 Cyprinidae. While • 

 in Erythnnus we perceive a most interesting link between the Physostomous 

 Teleosteans on one hand and the air-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 ia 

 likewise sub-divided by fibrous partitions, but whether such ate 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 

 some 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 



