ON THE ANATOMY OF FISHES. 
155 
changes in the internal capacity of the sacs can possibly occur, except in the direction 
of the long axis of each through movements of its outer wall ; and even if distension 
or contraction should take place in the latter direction, it is impossible that any 
motion could be imparted to the tripodes, by reason of the atrophy of the dorsal walls 
and the non-existence of the usual fibrous tracts by which such an effect is normally 
brought about. The extremely diminutive size of the air-bladder, when compared 
with the bulk of the I’ish, taken in conjunction with such facts in the structure of 
the organ as those indicated above, force us to adopt the conclusion that the air- 
bladder in Glyptosternum and Bagarius must be regarded as a vestigial and function- 
less structure — a conclusion which receives additional support from the existence 
of similar retrogressive modifications in the Weberian mechanism, and in those 
parts of the internal ear that are specially related to it. 
In our necessarily imperfect account of Ahysis and Acrochordonichthys there were 
several interesting points that we were unable to determine with certainty, of which 
the most important were, the condition of the dorsal walls of the air-sacs, and the 
presence or absence of a sinus endolymphaticus. We cannot but think, however, 
that our tentative conclusions with regard to those genera derive considerable support 
from the results of our investigations of Glyptosternum and Bagarius. From the 
strong resemblance between the four genera in all essential osteological details, as well 
as in the general structure and skeletal attachments of their air-sacs, and in the 
condition of the Weberian ossicles, we now entertain but little doubt that, so far as 
AJcysis and Acrochordonichthys are concerned, the agreement extends also to the 
atrophied condition of the dorsal walls, the suppression of the sinus endolymphaticus, 
and, in fact, to the rudimentary and functionless condition of both the air-bladder and 
Weberian mechanism. 
Glyptosternum conirostris, Steindachner. 
We could detect no essential differences between this species and the preceding. 
Euclyptosternum (sp. ?). 
In an undetermined species of this genus given to us by Dr. Day, we found the 
air-bladder and Weberian mechanism very similar in almost every detail to the 
coiTesponding structures in Glyptosternum. 
Ilara Buchanani. 
We have had no opportunity of dissecting this Siluroid, but according to Day (U) 
the air-bladder is “ rather large and situated in the abdominal cavity, not enclosed in 
bone.” It may, therefore, be concluded that the organ conforms to the normal Siluroid 
type. 
