connection to the optic nerve, the vitreous humor is usu- 
ally lost and the eyeball collapses around the lens. If 
this occurs, the outer fibers of the lens adhere to the 
inner coatings of the eyeball during fixation and are 
lost when the lens is removed. Discard damaged eyeballs. 
2. Lenses should not be allowed to freeze prior to 
or during fixing. Freezing frequently results in lens 
tissue being sloughed off. 
3. Lenses should be fixed in a buffered 10-percent 
formalin solution as soon as possible after the animal is 
collected. 
4. Ten days should be allowed for fixing lenses 
in the buffered 10-percent formalin solution. Our data 
suggest that no adverse effects occurred when eyeballs 
were left in the fixing solution as long as 120 days. 
5. After fixing, lenses should be dried for about 1 
week at 80° C. in an oven equipped with a fan for 
circulation of air. For an unknown reason some lenses 
and batches of lenses do not fix and dry properly. These 
lenses differ in appearance from those properly fixed, and 
with a little experience “bad” lenses can be quickly 
recognized. Discard any lens which evidences sloughing 
off of tissue or appears atypical in color or shape. 
Fig. 2—Mettler Gram-Atic balance. — 
This type of balance is suggested for 
weighing cottontail lenses for reasons 
of speed and accuracy. 
6. Because lenses are hygroscopic, they should be 
weighed immediately after removal from the drying 
oven or stored immediately in suitable airtight, moisture- 
free containers. 
7. Analytical balances of the Mettler type (Fisher 
Scientific Company, Pittsburgh, Pa.) (Fig. 2) are prob- 
ably the easiest and most rapid to use and the most 
reliable now available for weighing lenses; Roller-Smith 
precision balances (Roller-Smith Company, Newark, 
N. J.) have also proved satisfactory. 
LITERATURE CITED 
Dupzinsk1, M. L., and R. Myxytowyaz. 1961. The eye lens 
as an indicator of age in the wild rabbit in Australia. Com- 
monwealth Scientific and Industrial Research Organization 
Wildlife Research 6(2) :156-159. 
_ Lorp, Rexrorp D., Jr. 1959. The lens as an indicator of age 
in cottontail rabbits. Journal of Wildlife Management, 
23 (3) :358-360. 
This paper is printed by authority of the State of Illinois, 
IRS Ch. 127, Par. 58.12. It is a contribution of Illinois Federal 
Aid Project W-66-R, the Illinois Department of Conservation, the 
United States Bureau of Sport Fisheries and Wildlife, and the 
Illinois Natural History Survey, cooperating. William R. Ed- 
wards is Associate Wildlife Specialist, Illinois Natural History 
urvey. 
stu. 14 (45591—8M—12-67) : 
