Fig. 2. — Mettler Gram-Atic balance. 

 This type of balance is suggested for 

 weighing cottontail lenses for reasons 

 of speed and accuracy. 



connection to the optic ner\e, the vitreous hiunor 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 durina; fixing. Freezing freciuently results iti 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 clays should be allnwed for lixing 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 I 

 week at 80° C. in an oven ecjuipped 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 apjM'arance from those properly fixed, and 

 with a little experience "bad" lenses can be c]uickl\ 

 recognized. Discard any lens which evidences sloughing 

 off of tissue or appears atypical in color or shape. 



6. Because lenses are hygioscopic. 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 no\\- available for weighing lenses: Roller-Smith 

 precision balances (Roller-Smith Company, Newark, 

 N. J.) ha\e also proved satisfactoiy. 



LITERATURE CITED 



Oi nziNsKi, M. 1... and R. Mvkvtowvcz. 1961. The eye lens 

 as an indicator of age in the wild rabbit in .Australia. Com- 

 monwealth Scientific and Industrial Research Organisation 

 Wildlife Research 6(2) : 156-159. 



Lord. Rexforp 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, 

 Il'tS l^li, 127, Par. .iS.12. It is a oontritnition of Illinois Federal 

 .\iii rroject ^^'-^^(^-K. the Illinois Department of Conservation, the 

 I "nited States Hurcau .>f Sport Fisheries and Wildlife, and the 

 Illinois .Natural History Survey, eooperatinp. William R. Ed- 

 wards is .Associate Wildlife Specialist, Illinois Natural Historv 

 Survey. 



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