142 NUNNELEY, ON THE CRYSTALLINE LENS. 
weigh alike, a fact which I was not aware of until after all 
my experiments had been made. The tables show that, 
while there is a general agreement in the sp. gr. of the lens 
in animals of the same genus, there is a perceptible individual 
difference, which age alone will not entirely account for. In 
some few instances I have found the curious fact, that the 
sp. gr. of the two lenses, from the same creature, are not 
identical,* and the still more interesting one, that in such 
cases the size of the denser lens has been somewhat less than 
that of the lighter. This was well marked in the holibut, 
Nos. 6 and 7. They also show that in true land-creatures 
the sp. gr. of the lens is less than it is in water-creatures— 
the density of the lens of the duck, for instance, is decidedly 
greater than that of the common fowl—while the difference 
in that of the fish and the bullock and pig is very marked. 
The first table also shows that the lens is the densest of all 
the ocular tissues—and particularly so in the fish—where, 
from the density of the element from which it receives the 
rays of light, we should @ priori expect to find it so. 
Specific gravity. 
Bullock, entire eye ‘ : . 10411 
Lens taken from the same eye a2 5 . 11046 
Pig, No. 1, entire eye : : . 10803 
Lens taken from the same pig’s eye 11060 
Pig, No. 2, eyeball, with portion of optic nerve ‘attached . 11-0710 
Same eyeball without any optic nerve : . 105238 
Portion of optic nerve alone. ; - 1:0578 
Haddock, entire eyeball : ; - 1:0324 
Lens taken from the same eye . ; 11684 
The lens itself is also heavier than its capsule. The sp. gr. 
of a pig’s lens, without capsule, was 1:1015 ; with the capsule, 
1:0985. The average sp. gr. of four sheep lenses, with cap- 
sule, was 1:1152; of two lenses, without capsule, 1°1584. 
HUMAN LENS. 
1. Young adult man . 5 ; : : 11304 
2. Ditto : ; : : : 11304 
3. Adult woman : é , : 1:0909 
4. Ditto, : > . . 10967 
4) 44484 
Average ; : 11121 
o 
. Lens removed with anterior part of eyeball for disease of 
cornea of more than two years’ standing, which resulted in 
* Can this account for the fact of the focus of the two eyes differing, as is 
certainly the case in some persons, there being no perceptible difference in 
the appearance of the two eyes. 
