986 The American Naturalist. [December, 
becoming converted into limbs suitable for land locomotion, 
and in time developed into the lung- and gill-breathing batra- 
chia, and these in their turn into the lung-breathing reptilia, 
the locomotor organs gradually increasing in efficiency. Of 
these pre-batrachia, we have existing representatives in the 
mud-haunting Dipnoi, with their feeble limbs. In the great 
majority of the Ganoid fishes the bladder served but a minor 
purpose as a breathing organ, the gills doing the bulk of the 
work. In the Teleostean descendants of the Ganoids the - 
respiratory function of the bladder in great measure or wholly 
ceased, in the majority of cases the duct closing up or disap- A 
pearing, leaving the pouch as a closed internal sac, far a 
removed from its place of origin. In this condition it served 
as an aid in swimming, perhaps as a survival of one of its 
ancient uses. It gained also in certain cases some connec- 
tion with the organ of hearing. But these were makeshift 
and unimportant functions, as we may gather from the fact 
that many fishes found no need for them, the bladder in these ‘ 
cases decreasing in size until too small to be of use in swim- | 
ming; and in other cases completely disappearing, after 
having travelled far from its point of origin. In some other 
cases, above cited, the process seems to have begun again in 
modern times, in an eversion of the wall of the cesophagus for 
respiratory purposes. The whole process, if I have correctly 
conceived it, certainly forms a remarkable organic cycle 
development and degeneration, which perhaps has no counter- — 
part of similarly striking character in the whole range of 
organic life. 
