ox THE ANATOMY OF FISHES. 
187 
centrum of the first vertebra. We observed no indications of degeneration in the 
structure of the internal ear. 
At first sight it would seem that, so far as its air-bladder is concerned, Aspredo, 
while more closely resembling the normal Siluridm than any of the truly abnormal 
species that we have yet described, nevertheless presents an interesting connecting 
link between the two extremes. At any rate, this conclusion is suggested by the 
almost complete suppression of la.teral chambers, and the partial constriction of the 
organ into two laterally situated air-sacs. On the other hand, the air-bladder is by 
no means small in proportion to the bulk of the Fish ; and bearing in mind, also, that 
there are no obvious indications of retrogression, either in the Weberian ossicles 
themselves or their connection with the bladder, or in the condition of the internal 
ear, it seems reasonable to suppose that all these structures are as truly functional as 
in those species with more typical bladders. It may, therefore, be suggested that such 
an apparently retrogressive feature in the air-bladder of Aspredo as the practical 
atrophy of the lateral chambers is really related to the peculiarly flattened and 
shortened condition of the body, and is not to be taken as conclusive evidence of 
degeneration. At the same time, we admit that the atrophy of the lateral chambers 
must render the air-bladder and the Weberian mechanism less sensitive as a register 
of varying hydrostatic pressures.* 
Sub-Family SILURID.® HOMALOPTER^. 
Geoup ; — Clariixa. 
Clarias nieuhofii. 
Taylor (38) has given a brief description of the air-bladder of Clarias magur 
(under the name of Macropteronotus magur) to the following effect : — The bladder 
consists of two small pyriform sacs joined at their pointed extremities by an inter- 
mediate canal. The organ is said to lie across the spine, and each of its two pyriform 
portions to be contained in a funnel-shaped case projecting outwards from the side of 
the body of the “first” vertebra, and having its mouth covered over by the common 
integument, as in Pimelodus hagharia” (= Bagariiis Yarrellii). The case is formed 
of bone, but above and below by a tendinous membrane that extends across the inferior 
surface of the first vertebra, thus protecting from pressure the intermediate canal 
or isthmus by which the two pyriform sacs are united. A communication exists 
between the air-bladder and alimentary canal by a small ductus pneumaticus passing 
from the intermediate canal to the oesophagus. 
Cuvier and Valenciennes (8) refer to a species of this genus under the name of 
Clarias hasselquistii in which the air-bladder is described as being small and formed 
* Pli\ Biological section. 
2 B 2 
