THE BLIND FISHES OF MAMMOTH CAVE. 19 
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 Amblyopsis according to the generally recognized mode of 
its development (since it is ‘usually formed from an inv olution 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- 
eye of the blind fish, the anatomical characters which 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 c or any- 
thing analogous to an iris was detected, unless we regard as repre- 
senting the latter the increased number of pigment ‘alls. at the 
anterior part of the globe. 
It is said that the blind fishes are mga sensitive to sounds 
as well as to undulations produced by other causes in the water. 
In the only instance in which I ipro dissected the organ of hear- 
ing (which I believe has not before been anne) all its parts 
were largely developed, as will be seen by reference to Pl. 1, 
g.1 As regards the general structure, the Sails oe not differ 
materially from those of other fishes except in their popao 
dimensions. The semi-circular canals are of great | 
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 (Pl. 1, fig. 2) and seen in 
- *In birds and mammals there is a stage of development ma the lids —_ to- 
gether and firmly unite, to separate again animal “ In 
` the mole rat (Spalax typhlus) of Siberia, the lids never open, and t he eyes remai 
through life covered wee hairy 6 skin. It is o — grak: in er ae some- 
f tł e.—J.W. 
í tI have used the prior name of Branchiostoma in this sated when aan of the 
Lancelet 
