346 H. M. BERNARD. 
at the surface of slime wholly or partially produced by the 
excessive discharge of the pigmented granules. This refrac- 
tive mass, at first probably lying merely at the surface, would 
eventually be enclosed in an invagination, a phenomenon so 
common (e.g. in the formation of glands) that a discussion 
of the mechanics by which it might be brought about need not 
here detain us. 
The formation of a lens, the definite structure of which 
is now perhaps only indicated by the lengthening of the pali- 
sade cells as shown in the diagram, brought the pineal eye as 
an organ of sight to a high functional level. From this it has 
steadily declined, until it persists as a vestige which, in many 
cases, can no longer function in any way for the appreciation 
of variations of light intensity. 
In support of this interpretation of the morphology and 
physiological origin of the pineal eye, I would call attention 
to Spencer’s figures,! a study of which leaves no doubt what- 
ever that the pigmented cells are streaming from the connective- 
tissue capsule round the eye through the retina, just as in the 
rest of the skin they stream out from the cutis through the 
palisade layer of the epidermis. In the series of sections of 
Hatteria, kindly lent me by my friend Mr. Martin Wood- 
ward, in addition to the pigmented cells, there are others 
making their way alike through the retina and the palisade 
layer of the epidermis. These are cells containing enormous 
vacuoles which force the nuclei to one side. On reaching the 
horny layers these cells flatten out, and their vacuoles form 
flat spaces which give the cuticle a sort of false lamination. 
A still closer parallel between the pineal eye and the skin is 
observed in Uromastix, for the loan of sections of which I 
am again indebted to Mr. Woodward. Streaming through the 
cutis are innumerable cells laden with concretions which are 
black by transmitted, white by reflected light. They remind 
one of the guanin granules found in the tissues of Arachnids. 
Now, while the cells containing these white concretions do not 
seem to be able to pass through the palisade layer, but stop 
1 «Quart. Journ. Mier. Sci.,’ xxvii. 
