PROFESSORS T. W. BRIDGE AND A. C. HADDON 
bladder. In Scln'/hichfhys it will be noted that even the stem and inferior limb of the 
post-temporal may co-operate in securing this result. 
We have ventured to suggest this explanation in those cases where encapsulation is 
most complete, because at first sight it seems to be a legitimate inference from the 
three facts to which reference has just been made, but as an objection it may be 
urged that the same physiological result might have been gained by simpler and more 
natural means. Complete or partial atrophy of the air-bladder would even more 
effectually have prevented transmission of useless stimuli to the auditory organ, and 
would seem also to be the more natural as well as the more easily acquired safeguard. 
In some cases (e.g., Bafjarius, GJypiosternum, &c.) the latter method apparently is the 
one adopted for the purpose. But if our previous conclusion, that the useless air- 
bladder owes its singulai- persistence in these Siluroids to its connection with the 
'Veberian ossicles, be correct, it may nevertheless have happened that in other cases 
reduction in the size of the air-bladder took place so slowly that encapsulation super- 
seded complete atrophy as a means for securing the object in question. It must also 
be borne in mind that even in its normal condition the air-bladder and its connective 
tissue investment are frecpiently invaded by ossified deposit. The superficial ossifica- 
tion of the complex centrum and the ventral processes, the terminal plates of the 
“ elastic-spring ” apparatus, and the posterior extremities of the tripodes, are examples 
of this tendency. More or less complete encapsulation through an extension of this 
process may therefore have been moi'e readily ai;quired than at first sight would seem 
possible or probable. 
If it be objected that this view is somewhat far-fetclied, an alternative explanation 
of the difficnlty may be suggested. It is possible that encapsulation has really no 
physiological significance. Whatever share the modified transverse processes take in 
the process may be only due to their tendency to contract round and envelope an 
atrophying structure to an extensive portion of the suiTace of which they are always 
closely moulded, while the development of such additional means of encapsulation as 
the ossification of the walls of the air-bladder itself, or the growth of ventral pro- 
cesses, is due solely to an exaggeration of that tendency to ossification which is always 
obvious in the normal air-bladder when no longer checked in the useless organ by the 
controlling influence of natural selection. 
It is interesting to observe that other families of Ostariophyseae, and notably those 
Cyprinidae included in the sub-group Cobitidinae, exhibit a parallel, and in many 
respects a substantially similar series of modifications. As Weber [loc. cit.) first 
pointed out, the air-bladder of Cohitis fossilis is not only of relatively small size, but 
is also completely enclosed within a thin bony capsule of corresponding shape. Other 
Loach-like forms as, for example, Nemachilus and Botia, present the same peculiarity, 
and it is by no means improbable tliat a similarly modified air-bladder is present in 
all or most of the remairnng genera of this section of the family. In the three genera 
mentioned above the degeneration and encapsulation of the air-bladder follow much 
