•H 



INHERITANCE IN I .TINEA-PIGS. 



B hybrids, and in no case were hybrids from the two races bred with 

 h other. Nevertheless, the results obtained in the two cases were so 



Bimilar that for statistical purposes it was thought best to combine 

 ui. Race K is taken as the standard guinea-pig race with which the 



hybrids are compared. 



1 or a period <>t about a year and a half all cutleri individuals in the 

 laboratory, whether <>f pun- race or hybrids, were weighed two or three 

 times a month. In this way records were obtained from which growth 

 , , : , gee of weight, etc., can be deduced. The repeated and 



-went weighings allow the detection of periods of depression due to 

 illness or poor feeding. Due allowance has been made for all such 

 observations, as well as for increase in weight of females through 

 pregnancy. Nevertheless, observations on weight are at best not 



i 



dRaceB 



.Day$ 40 



SO 



120 



160 



200 



2-10 



2S0 



320 



360 



400 



I 1 



rowth-curves of C- cutleri and of race B guinea-pigs, the growth-curve of 

 each sex being shown separately. 



altogether satisfactory, since they are subject to fluctuation through 

 conditions of food, accumulations of fat when maturity has been 

 reached, etc. Greater value attaches to the bone measurements of 

 fully adult individuals (over 1 year old) so far as individual varia- 

 bility i> concerned. But the observations on weight afford a basis 

 entirely satisfactory for the determination of average sizes and average 

 growth curve- in different classes of hybrids. Incidentally they afford 

 ontrol on the bone measurements, for they indicate cases of abnormal 

 through disease, fighting, or other cause) and allow of either 

 remedying condition- or rejecting suspicious material. 



Pure ctUU n young of both sexes are of about the same average weight 



birth, vis, :>() grams (see fig. 1). The females at first grow a little 



than the male-, a fact perhaps correlated with their earlier sexual 



maturity. At about 50 days of age the two sexes are of practically the 



-lit. the male- having again caught up with the females, and 



