1879.] On the Morphology of the Semicircular Canals. 367 
to the maculz acustice of the ampullz and vestibule. They 
have received as yet no specific name. Leydig simply uses the 
expression “nerve-buttons” (nervenknopf), and F. E. Schulze 
nerve-hills” (nervenhuegel). In the adult forms of almost all 
fishes, these structures are inclosed in a continuous canal formed 
in the epithelium. To this fact we will return again. 
The function of these organs appears to be to appreciate mass 
movements of the water, and more particularly vibrations which 
have longer periods than those appreciated by the ear. 
Besides the similarity in the structure of the maculz of the 
lateral lines and the maculz acusticz, the following facts: indicate 
a close relation between the two sets of organs. In the first place, 
in accordance with the general law of the development of sensory 
structures,” both the ear and the mucous canals are developed 
from the epithelial layer of the embryo, namely, the epiblast: 
Secondly, the side organs of the head are supplied by the fifth 
pair of nerves, while those on the body are supplied by the lateral 
nerves, which in turn are made up to a greater or less extent of 
the fifth. Now, a fact, the significance of which can never be | 
over-estimated, is, that in the skate the auditory nerve is a primary 
branch of the fifth? 
Again, the organ of hearing is surrounded: by bone really 
belonging to the ectoskeleton, but usually becoming incorporated 
with the bones of the cranium. In the same manner the side 
organs of the head are surrounded by bones belonging to the 
ectoskeleton, and likewise becoming more or less incorporated 
with bones of the skull and face. The supratemporals, suborbitals 
and lachrymals are examples of these. Even in the side organs 
of the body the same tendency to the persistence of bone is 
manifested by the occasional presence of bone corpuscles and 
even of cartilaginous or osseous grooves or canals. Now, while — 
I recognize in this comparison only a very general fact, I still 
think that the parallelism between the bony support of the ear 
and the bony supports of the side organs is far greater than 
between the petrosal and the sclerotal. : 
Let us now turn to the development of the mucous canals, 
See Archiv f. Mikroskop. Anat., vi. F. E. Schulze, Ueber die Sinnesorgane der 
Seitenlinie bei Fischen u. Amphibien. - 
? See Am. Naturalist, Sep. No., 1878. The Sensory Organs, by the writer. Also 
Cosmos, 1878, Oct. and Nov.. Die Enstehung des Sinneswerkzeugs, by Professor 
Haeckel, ; a 
wen, Comp, Anat, of Vertebrates. 
