1892.] Contributions to the Anatomy of Fishes. 151 



Indications of retrogressive changes are not wanting in the auditory 

 organ. In some, at least, of the Siluridse abnormales the sinus endo- 

 lymphaticus has completely atrophied, although the cavum sinus 

 imparis and atrial cavities remain and retain their normal relations 

 to one another and to the scaphia. The Weberian ossicles, on the 

 other hand, are almost invariably complete. The few signs of degene- 

 ration which they exhibit relate to the straightness of the posterior pro- 

 cesses of the tripodes, the suppression of the ascending and condylar 

 processes of the scaphia, and, in a few instances, the absence of inter- 

 calaria. 



Taking into consideration the retrograde changes both in the air- 

 bladder and Weberian mechanism, it becomes almost impossible to 

 believe that any hydrostatic function can be assigned to these struc- 

 tures, or that they do otherwise than present various states of modifi- 

 cation towards the condition of vestigial and fuuctionless organs, and 

 this conclusion seems to us equally inevitable whatever may have 

 been their original function. 



Of the one hundred and sixteen genera mentioned in the 

 British Museum Catalogue no fewer than twenty-live at least are 

 referable to the Siluridee abnormales. 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 being at a con- 

 siderable 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, so that they 

 may be enabled to withstand the force of mountain torrents. Such 

 Fishes when not in motion probably rest upon or attach themselves 

 to the river bottom, and the uselessness and probable harmf ulness of 

 an air-bladder as a hydrostatic organ under such conditions is no 

 doubt the cause of its degenerate and rudimentary condition. 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 ; 

 similar habits characterise other forms. 



The susceptibility of the air-bladder to change of habitat or habits 

 on the part of its possessor is well shown by the variation that may 

 be met with in the same genus. Two species of Gryptopterus 

 (0. micropus and C. hexapiera) have rudimentary air-bladders, while 

 all the remaining species of the genus which came under our notice 

 have these organs unusually well developed. In two species of 

 Pimelodus also (P. pulcher and P. sapo) the air-bladder is not only 



