256 CLARKE. [VoL. II. 
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earlier stages of growth the number of diagonal rows was not 
much less than eight. 
The number of lenses constituting the visual surface of each 
eye ts variable, but not trregularly so. The smallest number 
noted is thirty-three, in a very young individual having but ezgh¢ 
rows; the greatest is eighty-eight, occurring in the single 
example mentioned, which bears e/even rows. 
Again, the number of lenses in successive rows is variable, 
but only so within certain well-defined limits. . In order to make 
this point clear, the following ten enumerations are presented, 
taken at random from a list of above three hundred tabulated 
eyes. 
ef 
3 
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1 
2 
3 
4 
5 
6 
7 
8 
9 
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It appears from this table that whatever may be the total 
number of rows in any eye, in the last four rows of lenses, and 
generally in the fourth from the last, the number of lenses is 
subject to very little variation, while the number in the first two 
or three rows may vary greatly. This variation is partially 
explained by the following fact: It will be found upon examina- 
tion of an average eye that the anterior edge is normally nearly 
vertical ; the vertical row following this edge is composed of 
four lenses. It is impossible for any lenses to be added to the 
anterior extremities of the diagonal rows terminating at this 
anterior margin, for new lenses are added only from the lower 
and upper margins of the visual surface (see further on). In 
ee 
a 
