bered consecutively and arranged by month. For exam- 

 ple, when one knows that a specimen was collected on 

 December 12 (day 346) and was estimated to be 216 

 days old when collected, one can estimate the date of 

 birth by subtracting 216 from 346, in this instance day 

 130, or May 10. Data on estimated dates of birth permit 

 computation of a mean estimated birth date and its 

 standard error and thereby facilitate testing of differences 



in these parameters among populations or comparison 

 with a normal as a means of determining differences 

 in age structure. 



SUGGESTIONS FOR HANDLING COTTONTAIL LENSES 



1. Care must be taken to remove eyeballs intact 

 (Fig. 1). When an eyeball is ruptured, frequently at the 



METRIC t 



8 





Fig. 1. — Cottontail 

 eye intact and eye 

 with lens removed. 

 The eyeball at left is 

 in the proper intact 

 condition after fixa- 

 tion in a 10-percent 

 formalin solution. The 

 fixed lens is shown 

 after removal but be- 

 fore dr\'ing. 



Table 2. — Figures for estimating birth dates of cottontails from the estimated age in days. 



