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 
3 
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 
8 
MICE atmo 
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 drying. 
TasLe 2.—Figures for estimating birth dates of cottontails from the estimated age in days. 
Day of 
Month Jan. Feb. March April May June July Aug. Sept. Oct. Nov Dec 
1 1 32 60 oT 121 152 182 PALS 244 274 305 395 
2 2 33 61 92 122 OS 183 214 245 21 306 336 
3 3 34 62 93 123 154 184 215 246 276 307 337 
+ 4 35 63 94 124 155 185 216 247 207 308 338 
5 5 36 64 95 125 156 186 PAM} 248 278 309 339 
6 6 37 65 96 126 157 187 218 249 279 310 340 
7 7 38 66 97 127, 158 188 219 250 280 Sybil 341 
8 8 39 67 98 128 159 189 220 251 281 312 342 
9 9 40 68 99 129 160 190 221 252 282 we 343 
10 10 41 69 100 130 161 191 222 253 283 314 344 
11 11 42 70 101 131 162 192 223 254 284 1e 345 
12 12 43 71 102 132 163 193 224 255 285 316 346 
13 13 44 72 103 133 164 194 225 256 286 sly 347 
14 14 45 U8: 104 134 165 195 226 257 287 318 348 
15 15 46 74 105 135 166 196 DET) 258 288 319 349 
16 16 47 75 106 136 167 197 228 259 289 320 350 
17 17) 48 76 107 137 168 198 229 260 290 321 351 
18 18 49 77 108 138 169 199 230 261 291 322 352 
19 19 50 78 109 139 170 200 231 262 Doe 323 353 
20 20 il 79 110 140 igi: 201 232 263 293 324 354 
21 21 52 80 tal 141 172 202 233 264 294 325 309) 
22 22 53 81 112 142 13 203 234 265 295 326 356 
23 23 54 82 113 143 174 204 235 266 296 327 Sayf/ 
24 24 55 83 114 144 175 205 236 267 297 328 358 
6) 25 56 84 115 145 176 206 237 268 298 329 359 
26 26 57 85 116 146 a7! 207 238 269 299 330 360 
ya | 2] 58 86 117 147 178 208 239 270 300 Sot 361 
28 28 59 87 118 148 179 209 240 271 301 332 362 
29 29 88 119 149 180 210 241 272 302 335 363 
30 30 89 120 150 181 Pilih 242 273 303 334 364 
ol 31 90 151 212 243 304 365 
