AUDITORY ORGANS. 
1205 
passes behind into a third semicircular canal , canalis 
posterior ( cp ), that bends upwards and afterwards for- 
wards and inwards, opening into the upper end of the 
superior sinus (.ss). 
The superior division of the organ usually com- 
municates by means of a small opening or a short tube, 
canalis utriculo-saccularis (cus), in the bottom of the 
utriculus, with the inferior division. The latter consists 
of a saccate part, sacculus (s), which in most fishes 
possesses behind a pouch-like appendage, lagena coch- 
leae (l), the first rudiment of the cochlea so richly deve- 
loped in the higher animals and, above all, in man, 
together with its highest development (the organ of 
Corti). From the inner superior side of the sacculus 
there issues besides a narrow canal, ductus endolympha- 
ticus, which as a rule lays itself on the membranes of 
the brain and terminates csecally, but sometimes, as in 
the Elasmobranchs, ascends to the upper surface of the 
head, where it has a free orifice. 
Of nerve-enclings the superior division contains at 
least 4, namely a large one in the bottom of the re- 
cessus utriculi ( macula ac. recessus utriculi , mu) and 
one in each of the three ampullae ( cristce ac. ampullce 
anterioris, externce, and posterioris, cr), besides which 
there appears in most fishes at the bottom of the utri- 
culus itself, in the neighbourhood of the opening into 
the sacculus, a small nerve-endiug ( macula ac. neglecta , 
mn). In the inferior division may be found, within 
the sacculus, a large ending ( macula ac. sacculi , ms) 
and in most cases another, posterior one ( papilla ac. 
lagence , pi), which is situated on the wall of the pouch- 
like cochlear appendage, as soon as this is developed. 
Thus in some fishes the number of nerve-endings is 
only 6, in others 7. These endings are everywhere of 
the same structure, the epithelium which lines them 
consisting of numerous cells (auditory or hair cells) 
furnished with hair-like processes (auditory hairs) pro- 
jecting freely into the endolymphatic fluid, and of 
supporting cells set between the former and isolating 
them. 
The acoustic nerve divides into several branches, 
which supply all these nerve-endings each with a bundle 
of nerve-fibres. These fibres, each of which issues 
from a bipolar ganglion cell embedded in the acoustic 
nerve and its branches, penetrate the epithelium of 
the nerve- endings and ramify around the auditory cells, 
over Avhich they spin free terminal ramifications, with- 
out being directly continuous therewith. 
Here we give some figures (fig. 362) to illustrate 
the various development of the auditory organ in carti- 
laginous and osseous fishes, namely Cliimcera, Acipen- 
ser, and Perea, adding a figure of Scylliorliinus to show 
further how the organ has developed a special type in 
the Sharks and Rays. The auditory organ of the Lung- 
fishes and amphibians is most closely linked, among 
the forms adduced here, to the Ganoid type, as shown 
by fig. 362, E , which represents the appearance of this 
organ in Siren lacertina. The present, however, is no 
suitable opportunity for a, closer consideration of these 
questions. 
From the above it appears that, as we have al- 
ready pointed out, the auditory organ of Myxine may 
justly be regarded as the lowest known form of the 
development of this organ among the vertebrates, but 
that, the intermediate links being absent, we can only 
imperfectly sketch its phylogenesis. In Myxine a di- 
vision into a superior and an inferior part has pre- 
sumably not yet taken place, and the inner part of the 
annular tube probably represents both utriculus and 
sacculus, which is also indicated by the emission from 
this part of the endolymphatic duct. The outer part 
of the annular tube probably answers to the anterior 
(or the outer) and the posterior semicircular canals with 
their respective ampullse. Possibly in the future, when 
the development of Myxine has been brought to light, 
some knowledge may be gained both of this question 
and so many others, touching the systematic position 
of this remarkable creature and its relation to the rest 
of the vertebrates. 
In the anatomical structure of Myxine we have 
still to consider the organs of generation and in con- 
nexion therewith the present knowledge of the im- 
pregnation and development. 
The structure of the ovary and eggs has long been 
known. In the abdominal cavity of most specimens is 
found along the right side of the intestine a somewhat 
lobate, longitudinal mesentery, within which are en- 
closed, as it were suspended, rather numerous ova of 
varying dimensions. In small individuals these ova are 
generally of insignificant size and rounded form, some 
hardly visible to the naked eye, other somewhat larger, 
up to the size of a pin’s head. In more full-grown 
individuals many similar eggs are also found, but there 
besides appear, as a rule, a number (10 — 15 or more) 
of larger ova, which are always oblong, fusiform, mea- 
suring in some cases only 3 — 10 mm., in others 11 — 12 
