ON THE ANATOMY OF FISHES. 
305 
function no longer exists, and the extraordinary variations which they often exhibit 
in different Siluridse abnormales can only be regarded as furnishing abundant 
illustrations of the extreme variability to which all degenerate and useless organs are 
liable. 
The widespread degeneracy of the air-bladder in the Siluridse is amply proved by 
the fact that of the one hundred and sixteen genera mentioned in the British Museum 
Catalogue of the family, no fewer than twenty-five are referable to the Siluridae 
abnormales, and it is extremely probable that further investigation, especially among 
the various mailed Loricaroid forms and their naked allies, will considerably add to 
the number of Siluridae with degenerate and functionless air-bladders. 
The causes that have led to the degeneracy of the air-bladder in so many forms are 
in many instances not difficult to trace, and, as in so many Physoclist Teleostei, the 
assumption of a purely ground habit of life is probably the most important one. Not 
a few of the genera of Siluridae abnormales inhabit the comparatively shallow waters 
of rapidly flowing mountain streams and torrents, often living at a considerable 
altitude, and in general habit are not unlike our common English Loaches. Many 
are provided with an adhesive apparatus on the ventral surface of the body between 
the pectoral fins for attachment to stones, so that they may be enabled to withstand 
the force of mountain torrents. Such Fishes when not in motion by the exercise of 
their fins probably rest upon, or attach themselves to, the river bottom, and the utter 
uselessness and probable harmfidness of ait air-bladder as a hydrostatic organ under 
such conditions is no doubt the cause of its degenerate and rudimentary condition 
in such Siluroids as Sisor, Pseudecheneis, Glyptosternum, Euclyptosternum, Exo- 
stoma, Amblycep)s, &c. Although very different from the latter in the character 
of their habitat a similar explanation will jtrobably apply also to such widely dis- 
similar forms as Callichthys and Clarias. Various species of Callichthys are said* to 
keep under plants in marshy swamps, to be able to burrow in the mud, in which they 
often become dried up, and even to be capable of migration upon land in search of 
water. On the same authority Clarias magur is said to often frequent ponds and 
ditches, and, when the water dries up, to become imbedded in the mud, where it 
sojourns until the advent of the next rainy season. The same species is said to 
possess exceptional vitality when removed from its natural habitat. From their 
partially amphibious and grovelling habits it is clear that an air-bladder can be of 
little use to these Fishes as a hydrostatic organ, and hence its rudimentary condition. 
Similar remarks will in all probability apply to such other Clarias-\\ke forms as 
Saccohranchus and Ileterohranchus, and probably also to many other Loricaroid 
types in addition to Callichthys, about which we have not been able to glean much 
positive information as to their habits. The position of the mouth and the retro- 
verted and Loach-like character of the lips in so many Loricaroid genera is strongly 
suggestive of their grovelling habits, and the consequent uselessness of an air-bladder. 
* Clvikr et Vai.knciennes (8), vol. 15, pp. 219-220; also p. 228. 
.MDCCCXCIIf. — f5. 2 R 
