62 BULLETIN OF THE 
as representiug the “choroid gland.” The evidence for this is princi- 
pally in the position which it occupies, and very little in its structure. 
It is true that this body may contuin a small amount of pigment in the 
normal eye, as I find to be the case in Clevelandia, yet its characteristic 
structure consists, as is well known, in its richness in blood-vessels ; but, 
as already said, none of these occur in Typhlogobius. Its position — viz. 
at the proximal pole of the eye at or very near the entrance of the optic 
nerve, and between the chorio-capillaris and the sclerotic — is, however, 
strong evidence in favor of regarding it as the “choroid gland.” This 
structure is described in text-books (Wiedersheim, ’86, p. 412) as being 
situated in the normal fish eye between the argentea and the pigmented 
layer of the choroid. The fact that no argentea is present in the eye of 
Typhlogobius weakens somewhat the force of the evidence that I have 
used to support the assumption that I have made with reference to the 
significance of the pigment mass described. But its relation to the 
chorio-capillaris and the pigment layer of the choroid are the same as 
that of the “choroid gland”; as is also its relation to the sclera, with 
the exception that no argentea is interposed between the two. Of 
course it is impossible to say that, were the argentea developed, it would 
lie between the sclera and the pigment mass, rather than between the 
lgtter and the pigmented layer of the choroid. "We however have as 
much reason to suppose it would occupy the former position as the latter. 
The pigment layer of the retina is exceedingly thick. In a specimen 
about 50 mm. long, the entire thickness of the retina including the pig- 
ment layer was 0.108 mm., and that of the pigment layer was 0.07 mm.; 
while in a specimen of Clevelandia of about the same length, the entire 
thickness of the retina including the pigment layer being 0.13 mm., 
the thickness of the pigment layer was only 0.037 mm.; that is, in 
Typhlogobius the thickness of the whole retina is to the thickness of the 
pigment layer as 1.5 : 1, while in Clevelandia the corresponding ratio is 
3.5:1. In Gasterosteus, I find that about the same proportion holds 
as in Clevelandia, whereas in the perch (H. Müller, ’57) the proportion 
is at least not less, and in the salmon a year old (Hoffmann, '83) the 
proportion is 64- : 1. 
The layer is composed wholly of pigment of the dark brown granular 
variety. I have searched in vain for cellular elements within it, In 
most specimens the pigment is a very uniform mass; but occasionally 
one finds an eye in which very distinot and perfectly round nodules of 
pigment occur. Some of these are so clear-cut and smooth in outline 
that they have the appearance of perfectly round cells wholly trans- 
