1879.] On the Morphology of the Semicircular Canals. 309 
are an order which is comparatively very young, not making its 
appearance until the Cretaceous period. Observe how these facts 
accord with the development of the lateral line. In Teleosts the 
involution of the maculz or nervehills of the lateral system and 
the consequent formation of a canal, does not take place for days 
and even weeks after the young fish has left the egg. In one 
instance, Gobius minutus} it does not take place at all. In Elas- 
mobranchs, however, as stated, the canal is already formed in the 
embryo. 
Surely such a harmony of facts must be of significance, and 
they must open our eyes very widely with regard to the relation 
between embryological and race development, or, to use the words 
of Prof. Haeckel, between ontogeny and phylogeny. Doubtless 
in the primitive Elasmobranchs, or in their ancestors, the develop- 
ment of the mucous canals was similar to that of the Teleosts of 
the present day, but, in the countless repetitions during countless 
ages, the process was shortened and made, as we find it, imme- 
diate and direct. 
Now, what bearing have such facts as these on the correct 
understanding of the embryology of the ear?. Let us see. 
Can we suppose that a structure as old as must be the organ of 
hearing, is still formed in the embryo by repeating the various 
stages once traversed by our remote ancestors ? Would it not be 
more philosophical to expect that this organ is now produced by 
a process more or less direct? To this latter view I think we 
must, by necessity, incline. 
The embryology of the ear may be briefly stated, as follows: 
It first makes its appearance as a depression of the epiblast in the 
neighborhood of the hind-brain. This depression gradually deepens 
until, by the coalescence of its edges, it is converted into a closed 
cavity. This cavity then rapidly enlarges and certain dilations 
or protrusions of its surface into the surrounding mesoblast take — 
place. These protrusions are severally converted into the semi- 
circular canals and cochlea. In the case of the semicircular 
canals each dilatation becomes flattened, and, by the meeting — 
and coalescence of its opposite walls in the middle, its peripheral 
portion is converted into a tube, both ends of which remain per- 
manently in communication with the primitive vesicle. The 
cochlear protrusion undergoes no such transformation but is sim- 
ply prolonged, forming the true membranous cochlea or scala 
1See F. E. Schulze, loc. cit. fou 
