PISCES. 
The tissue of which they are composed is similar 
to that which forms the membranous vestibule 
and saccus ; it is, however, a tissue sui generis, 
being neither exactly comparable to cartilage, 
nor tendon, nor cellular membrane. It is pel- 
lucid, and when emptied of the enclosed fluid, 
inelastic, but flexible and easily torn. Its 
thickness is greater than that of the vestibule or 
of the sac of the otolithe; but the ampulle 
seem thicker than the rest, for when wounded 
and their contents allowed to escape they still 
retain their form and expansion. 
The membranous labyrinth is filled with a 
limpid fluid. 
Auditory nerves.—The labyrinth of the ear 
in Fishes receives its nerves from two sources,* 
1st, from the auditory nerve, properly so called, 
which is distributed to the membranous vesti- 
bule, and to the ampulle of the anterior and 
external semicircular canals; 2ndly, from the 
“‘accessory auditory nerve,” which, in most 
instances, seems to arise not from the brain but 
from the trigeminal or the vagus nerve, and 
supplies the ampulla of the posterior semicir- 
cular canal and the saccus. 
Ear of plagiostome cartilaginous Fishes.— 
In the Skate are two canals, regarded by Monro 
as representing the meatus auditorius externus. 
The orifices of these are situated at the upper 
and back part of the head at a short distance 
from the junction of the skull with the first cer- 
vical vertebra, the opening of each being large 
enough to admit the end of a probe. Each of 
these orifices leads to a winding canal about 
two lines in diameter, which, after describing 
more than three-fourths of a circle, may be 
traced into the membranous vestibule of the 
ear. This canal is generally found filled with 
a white viscid matter. The vestibule is a large 
sac containing a very viscid pellucid humour, 
in consistence like the white of an egg, in 
which is suspended a soft cretaceous substance. 
To the anterior part of the large sac there is 
a smaller compartment communicating with the 
former by a narrow passage, which is likewise 
filled with glairy fluid, and, posteriorly, there is 
a third very small sacculus, similarly distended, 
in both of which cretaceous matter is found. 
The remaining portion of the internal ear 
consists of three canals, analogous to the semi- 
circular canals of the higher Vertebrata, but 
which here rather deserve the name of circular, 
seeing that each forms a complete circle; of 
these the anterior and the middle are joined 
together at their commencement by the wide in- 
tercommunicating branch which opens through 
the intervention of a small membranous tube 
into the anterior small sac of the vestibule. 
The third or posterior canal communicates with 
the large sac of the vestibule by means of a 
wide canal, but has no direct communication 
with either of the others. 
Each circular canal has a dilated portion or 
ampulla near one of its extremities, and is filled 
with a pellucid viscid fluid. They are all con- 
tained in cartilaginous tubes excavated in the 
cartilaginous substance of the cranium, but 
* Weber, loco cit. 
1005 
much wider than the membranous canals them- 
selves, the latter being suspended in a fluid 
interposed between them and the perichondrial 
lining of the cartilaginous passages, to which 
they are fixed by a delicate cellulosity, in which 
slender vessels and very minute nerves are 
visible. 
The auditory nerve on entering the ear di- 
vides into several branches. Of these the prin- 
cipal spreads out upon the inferior aspect of 
the great sac of the vestibule, where it forms a 
rich plexus; a similar but smaller plexus is 
formed upon the smaller anterior sac commu- 
nicating with the vestibule, while the other 
branches are appropriated to the semicircular 
canals, on the ampulle of which they would 
seem to be exclusively distributed; at least 
after forming a very beautiful expansion upon 
the dilated portion of the canal, it is impossible, 
owing perhaps to their very minute size, to 
trace them any further over its cylindrical part. 
Generative system—One of the most re- 
markable circumstances connected with the 
history of the finny tribes is their extreme 
fertility, which, compared with that of the 
higher Vertebrata, is truly prodigious. A cod- 
fish has been calculated to produce 9,000,000 
of eggs in a single season, and innumerable 
races of the osteopteryginous Fishes exhibit 
per of reproduction equally extraordinary. 
© imagine that this exuberant fecundity is 
destined merely for the purpose of perpetuating 
the species would evidently be preposterous, 
and we are necessarily led to look for other rea- 
sons explanatory of such teeming births. There 
is this leading difference between the terrestrial 
and aquatic domains of animated nature—the 
earth is inhabited only at its surface, and the 
vegetable banquet which is there spread out in 
such rich abundance is sufficient to afford the 
means of subsistence to all earth’s progeny. 
But the sea, throughout all its depth, at every 
altitude which man has been able to explore, 
is peopled with innumerable races of voracious 
beings, all of which are necessarily dependent 
for their existence upon a supply of animal 
food, which must consequently be distributed 
as widely as the waves of ocean are diffused. 
It is to supply this great stock of living pro- 
vender that the Sponges and the Polyps and 
all the humbler marine forms of existence are 
continually pouring forth their multitudinous 
germs, and it is for the purpose of adding to 
this enormous store that the majority of the 
osseous Fishes are so inordinately prolific. 
From these considerations we perceive at 
once a reason for the extraordinary apathy and 
total absence of parental affection which forms 
so conspicuous a feature in the character of the 
whole race, and it is by no means a subject 
devoid of interest to observe how gradually 
the ties between parent and offspring are drawn 
closer and closer as we ascend from these 
humblest members of the Vertebrata and arrive 
at progressively increasing intelligence as we 
advance from class to class. 
The generative apparatus of Fishes, as we 
have pointed out in a preceding article, (Gr- 
NERATION, OrGaxs oF, Comp. Anat.,) pre- 
