538 FRANOIS VILLY. 
with the cochlea as in the frog; but they differ from both 
frog and toad in that they communicate with each other 
within the capsule, and then pass out by a common duct into 
the skull. Just where this duct enters the skull a dilatation 
is present passing through the foramen of the glossopharyn- 
geal nerve, and lying close above the pharynx as in the frog 
and toad. I may mention that my Dactylethra specimen 
seems to show a continuity of these canals of the two sides 
across the floor of the brain-case. I feel sure that this is not 
so in the other animals examined, and this, together with the 
imperfect condition of my Dactylethra makes it very doubtful 
whether any such connection really exists. 
The most interesting point in the development of this 
system is that in both cases the canals first appear in close 
connection with the parts of the cochlea with which they are 
ultimately to be associated. At about 16 mm. the lagena 
becomes flattened as in the adult, and the beginning of its canal 
is to be seen as a small sac in the perilymph applied to the 
lagena as already mentioned. It is formed by mutual separa- 
tion of the mesoblast cells in the vicinity of the lagena, and 
the cells so separating constitute the walls of the canal. The 
second canal appears soon after in a precisely similar manner, 
and the two grow towards the brain, meet and unite. The 
srowth of the auditory capsule and skull occurring at this 
time, separates the inner ear permanently from the portion of 
the canals within the skull ; at the same time foramina are left 
through which the communicating ducts pass. 
It seems most probable that the canals here described have 
some connection with the conduction of sound. From their 
mode of development and their permanent form it is evident 
that they are concerned with the cochlea, and it is very possible 
that the part lying outside the skull above the pharynx receives 
vibrations and permits their passage to the auditory labyrinth. 
If this is the function that the canals perform they must have 
been employed in this manner before the columella appeared 
and still remained in use after the terrestrial character and 
structure were acquired, 
