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PROFESSORS T. W. BRIDGE AND A. C. HADDON 
ascending processes are invariably wanting. As regards its position, the relations of 
the crescentic process of the trIpus to each lateral air-sac are precisely similar to those 
of the same structure in each half of the anterior chamber In a normal Silm’oid, but in 
shape It is variously modified. Very rarely does it retain its characteristic sickle-like 
form, more frequently it is nearly straight, with a pointed distal extremity {c.g-, 
Bagarius), or but slightly curved {eg., Glyptosternum) ; exceptionally {e.g., Clarias), 
the crescentic process is curiously angulated and heeled. A ventral ridge is rarely 
present — a fact which must be associated with the general thinness of the walls of the 
air-bladder, and the occasional degeneration of those fibres which normally converge 
from the dorsal wall and are inserted into it. The articular process of the tripus is 
usually long and tapering, with a pointed distal extremity, and retains its usual 
relations with the anterior portion of the complex centrum. The anterior process 
presents no special characters. Iladial fibres can generally be detected, but in some 
cases are less obviously specialized than in others, and, where radial nodules are 
absent, pass directly from the lateral surfaces of the complex centrum to the inner 
or faintly concave margins of the crescentic processes of the tripodes. On the other 
hand, in those Siluroids in which the dorsal wails of the air-sacs have degenerated, 
radial fibres, if present at all, are very feebly developed {e.g., Bagarius, &c.). 
Lateral cutaneous areas are almost invariably well marked, and, as a rule, close the 
distal openings of the osseous recesses in which the air-bladder is lodged, but their 
relation to the outer walls of the latter vary considerably. In some forms the two 
structures are in close contact {e.g., Clarias, Calloniystax), but more frequently they 
are separated by a considerable interval, which is usually occupied by the lateral lobes 
of the liver, or even, in addition, by the mesonephros or its anterior lymphoid portion 
— the head-kidney.” 
A ductus pneumaticus may be present or absent. It is usually present when the 
laterally-situated air-sacs are connected by an intermediate tubular portion {e.g., 
Ckaias, Saccohranchus, and others), but it is absent when the two sacs are com- 
pletely separated or connected only by a solid fibrous band {e.g., Bagaruis and 
Glyptosternum). Larely is it represented by a solid fibrous cord. 
Our investigations into the structure of the auditory organ in this section of the 
family are not so complete as we could desire, and our regret is the greater because it 
would have been extremely interesting to ascertain how far the atrophy and degene- 
ration of the air-bladder is correlated with similar retrogressive changes in those 
portions of the membranous labyrinth which are functionally related in the Weberian 
mechanism. That our specimens were not sufficiently well preserved to admit of 
accurate research on this point, is due to the fact that many of them had been 
])reserved for some considerable time without being previously opened to secure the 
proper permeation of the specimens by the preservative fluids. In some genera {e.g., 
Bagarius, Glyptosternum, Euclyptosternum, Acrochordonichthys, and Ahjsis) we 
entertain but little doubt that degeneration of the air-bladder is accompanied by 
