260 CLARKE. [Vot. II. 
has been seen to indicate the fact that the cavity of the cornea 
was not szmple, but compound. (May the posterior cavity-fillings 
represent the position of the anterior extremities of crystalline 
cones ?) 
MULTIPLICATION AND DIMINUTION IN THE NUMBER OF 
LENSES. 
The lenses of the visual surface are not all of the same size 
in any of the stages of growth observed. The size of the fully: 
developed lens varies according to the individual development 
of the animal; z.¢., the larger the animal, the larger the lenses ; 
but in any given subject some lenses are to be found which are 
below the average of size for that eye. These small lenses are 
found at the extremities of the diagonal rows which terminate 
on the posterior portions of the upper and lower margins of the 
visual surface. 
The inferior size of these lenses is due in part to unlike causes. 
Of these the principal cause is (a) that they are new and imma- 
ture lenses added in regular order to the ends of the rows of 
older lenses. It has not been as yet satisfactorily determined 
whether the increment of new lenses may take place at either 
upper or lower extremity of the diagonal rows, although the 
small lenses occur indifferently at either end. There is no 
reason to doubt that this addition does take place at the lower 
extremities, but on account of the close juxtaposition of the 
palpebrum to the upper margin of the visual surface, it may be 
questioned if at any period of growth sufficient room is allowed 
in this region for additional lenses. 
A secondary reason for the small size of the lenses is (4) the 
constantly increasing size of the interlensar sclera after matu- 
rity, which gradually envelops the lenses especially along the 
upper margin of the visual surface, where, by coming into con- 
tact with the increasingly prominent palpebrum, the lenses are 
often nearly concealed. 
To what degree the small size of the lenses along this upper 
margin may be due to the overgrowth of the sclera, and how 
much to the possibility of their being newly developed, it has 
been impossible to ascertain, but that it is due to acertain degree 
to both causes, is shown by the following facts: (1) immature 
