42 
EYES AND EAllS OF THE BLIND FISH. 
for the most part with the retina. All of the parts just enumer- 
ated are such as are ordinarily developed from and in connection 
with the encephalon, and are not in any way dependent upon the 
skin. But if the lenticular-shaped body is the true representative 
of the crystalline lens, it becomes difficult to account for its pres- 
ence in Ambl 3 "opsis according to the generally recognized mode of 
its development (since it is usually formed from an involution of 
the skin) unless we suppose that after the folding in of the skin 
had taken place in the embryonic condition, the lens retreated from 
the surface, and all connection with the integument ceased. 
According to Quatrefages, however, the eye of Amphioxus [|] 
is contained wholly in the cavity of the dura mater, and yet it has 
all the appearance of being provided with a lens. If his descrip- 
tion be correct, then the mode of development as well as the mor- 
phology of the eye in this remarkable fish is different from that of 
most other vertebrates, since the lens never could have been 
formed from an involution of the skin, nor could the eye with its 
lens, as Prof. Owen asserts, be a modified cutaneous follicle. 
Whatever views be taken with regard to the development of the 
eye of the blind fish, the anatomical characters wdiich have been 
enumerated show, that though quite imperfect as we see it in the 
adult, it is constructed after the type of the eyes of other ver- 
tebrates. It certainly is not adapted to the formation of ima- 
ges, since the common integument and the areolar tissue which are 
interposed between it and the surface, would prevent the transmis- 
sion of light to it except in a diffused condition. No pupil or any- 
thing analogous to an iris was detected, unless we regard as repre- 
senting the latter the increased number of pigment cells at the 
anterior part of the globe. 
It is said that the blind fishes are acutely sensitive to sounds 
as well as to undulations produced by other causes in the water. 
In the only instance in which I have dissected the organ of hear- 
ing (which I believe has not before been noticed), all its parts 
were largely developed, as will be seen by reference to PI. 1, 
fig. 1 e. As regards the general structure, the parts do not differ 
materially from those of other fishes except in their proportional 
dimensions. The semi-circular canals are of great length, and 
the two which unite to enter the vestibule by a common duct, it 
will be seen, project upwards and inwards under the vault of tlie 
cranium, so as to approach quite near to the corresponding parts 
of the opposite side. The otolite contained in the utricle was not 
remarkable, but that of the vestibule (PI. 1, fig. 2) and seen in 
^In birds and mammals there is a stage of development where the lids come to- 
gether and firmly unite, to separate again when the animal “gets its eyes open.” In 
the mole rat {Spalax typlilus) of Siberia, the lids never open, and the eyes remain 
through life covered with hairy skin. It is not improbable that in Amblyopsis some- 
thing analogous to this, a closing of the skin over the eye, may have taken place.— J. W . 
1 1 have used the prior name of BrancMostoyna in this paper when speaking of the 
Lancelet. 
