F2 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTURE. 
ALLOWANCE FOR AGE OF DAM. 
‘Another conceivable cause of differences among the experiments is 
the percentage of litters produced by immature females. The per- 
centage of first litters in each experiment is shown in Table 6. 
TABLE 6.— The first litters from immature parents (mated at one or two months of age) as 
percentages of the total number of litters (1916-1919). 
Experiment. oer || Experiment, ee Experiment. ao Experiment. noe 
| 
Bk xtss sees SAR UA iSO. us poset 1 Stall CON pean ee ZUG Clie veer 20. 5 
PS ons See eae 1858, Others .2252 ee |) <iethOs 28 |eOsAt oo Sete ee Pater ROP eee mene 25.3 
2S! Paste 18.4 || Inbred.........| D745 )|PA CG cas oe oe 20.3183 CL. Mee ees 25. 4 
BOree ons eae ane PYAR SGN i S Yeeatenge te apa aay =o a |e OL Oe ea a L6ESE CG Ree ee 23.8 
Assuming that first litters are at a disadvantage, Experiment B 
should be superior to the inbreds, Experiment CC should be practi- 
cally the same, while the other crossbreeding experiments should be 
inferior. However, as pointed out in Part I, the slight inferiority of 
first litters found in the present stock of guinea pigs is almost wholiy 
a seasonal complication. A majority of the matings have been made 
in summer and fall under favorable conditions, bringing a majority 
of the first litters in winter and spring,.when conditions are apt to be 
poor. It is found that on making proper correction for season, the 
low records for first litters born when the female is about 6 months old, 
as well as the similarly low records near 18 months of age, are brought 
almost to the 12-month and 24-month levels. It may safely be as- 
serted that the differences in the average age of the dams in the 
various experiments are negligible as causes of differences in their 
records. . RS 
ALLOWANCE FOR SEX. Ce 
There is a slight difference between the birth weight of males and 
females and a slightly greater difference in their weaning weights. 
Since, however, the sex ratio (Table 7) in no case departs widely from 
equality, it Was not been deemed necessary to find separate averages 
for the sexes. 
TABLE 7.—Sex of young born in each experiment, 1916-1919. 
{Those of unknown sex were in general found dead and in bad condition.] 
{ 
| 
Sex Males — Sex ales 
pen | Males ae un- | Total. | per 100 | eas Males. ES. un- | Total. | per 100 
* | known. females. | ‘| known females 
ae 514 444 40 998 TOIESES |} (CLG ges ae 297 303 17 617 98. 0 
Dae 350 361 29 740 97.0 | Cl. 302 317 10 629 95. 3 
Pa e See 237 245 | 6 488 9627315 C2:- a 94 87 1 182 108.0 
Re Spee 429 398 6 833 107.8 ——— — 
DONS ae | 195 177 10 382 IMOS2 RCs os 183 186 12 381 98. 4 
CGS 285 277 19 581 102 9 
Other... =| 564 567 39} 1,170 99. 5 | = 
Inbred... 2,289 | 2,192 130 |} 4,611) 104.4 || B....... 761 762 36 | 1,559 99.9 
Coe eel 653 647 34; 1,334 100.9 | | SS SS 
CR Te | 206 202 | 2} 7410! 1020 | Total..) 5,341 | 5,262| 272 | 10,875| 101.5 
AGEL 27 289 | 11 571 93.8 | 
