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with the lungs of Batrachians and other air-breathing verte- 
brates appears to be proved. Among the Teleostean fishes the 
air-bladder exists as a closed sack of diverse forms. These 
forms are termed Physoclisti. In such forms as swim near the 
surface the air-bladder is mostly of comparatively small size, 
while in those that live near the bottom, Plewronectide, it is, as 
a rule, absent. 
The chief uses of this organ in Teleostean fishes appear to 
be two. (1), for flotation, enabling its possessor to maintain a 
certain level in the water; and (2), for acoustic purposes, it 
being partially or entirely employed for hearing, by means of 
various modes of connection with the internal ear. 
It seems to be the rule that the fresh-water Physostomi have 
a connection, by means of a chain of ossicles, between the 
air-bladder on one side and a process of the internal ear on the 
other. These auditory ossicles were first pointed out by WEBER. 
The chain of auditory ossicles connecting the air-bladder with 
the internal ear were, as far as known to the Doctor, confined 
to the fresh-water Cyprinidae, Characinide, and Siluride, though 
he thought it probable that this chain of ossicles will be found 
in other fresh-water families which he had not had the oppor- 
tunity of investigating. 
In conclusion the Doctor affirmed his belief that the air- 
bladder of fishes is the homologue of the lung of the superior 
vertebrate forms; that in some of the higher sub-classes it 
serves aS an accessory respiratory organ for depurating the 
blood, and that with the majority of the Teleostean fishes it 
serves both as a float and as an organ of hearing. 
The next subject was “‘The Modern Classification of Ammon- 
ites,’ by Dr. Wricut, who is the author of the elaborate 
monograph “The Lias Ammonites,” now in progress of 
publication by the Paleontographical Society of London. 
Dr. Wricut, F.R.S., introduced his paper on the Modern 
Classification of Ammonites with a general outline of the 
anatomy of the structure of the Nautilus pompilius, and its 
polythalamous shell, and the relations subsisting between them, 
inasmuch as it is the only living representative of the group of 
