LO 



INHERITANCE IN GUINEA-PIGS. 



M times; litten of I have been recorded 18 times, litters of 3, 10 times, 

 md .i litter of 4 once. Factors which influence size of litter are evi- 

 dently age and state of nourishment of the mother. Table 2 shows the 

 relation of age of mother to size of litter. Very young mothers (age 

 •I months Of lees) have only 1 young at a birth. The females become 

 wallv mature a1 a very early age, as do female guinea-pigs. Well- 

 Dourifthed females may breed at 2 months of age, when they are less 

 than half-grown, full growth not being attained until they are 12 or 13 

 months old Females over 4 months but under 12 months of age 

 produce usually 1 or 2 young at a birth, rarely 3; those which are 1 or 

 Id produce the maximum number of young, usually 2 or 3, 

 rarely 1 or 4. After the age of 2 years the number of young again 



Table 2. — Relation between age of mother and size of litter, Cavia cutleri. 



decreases to 1 or 2. The oldest female known to have borne young 

 4 the original stock) had at the time been in captivity over 2 

 and her estimated age was 32 months. None of the females 

 horn in captivity has given birth to young at a more advanced age 

 than 29 months. Our records accordingly indicate that females rarely 

 ed after fchey have attained the age of 2\ years. The duration of 

 the breeding period in the case of males is more extended. It is prob- 

 able that males •!<> not attain sexual maturity quite so early as females, 

 f<»r females may breed when less than 2 months old, but we have no 

 denoe that males can breed before they are 3 months old. 1 But the 

 capacity t.» breed once attained continues indefinitely. One male 

 * 1 caught wild in December 1911 and estimated then to have been 

 tenths old Lb -till siring young, more than 3 years after his capture, 

 being, it U .--timated, nearly 4 years old. 



males are capable of breeding again immediately after the birth 

 i. but if they do bo the number of young at the next birth is 



Dtion (o a record from his experiments which shows that a male 



light infusbo <.f r blood must have been sexually mature at 2J 



- the only record known to me of a guinea-pig male breeding when lesa 



