

INHERITANCE IN I ;UINEA-PIGS. 



hybridization ha* no! been retained in the second-generation offspring, 

 which -ink as regards weight to a position intermediate between the 

 part-ni races. N evert hclcss the F a hybrids are nearer to race B than 

 to cutlery in adult size, which fact suggests that not all the growth 

 ,„,; furnished by hybridization has yet been dissipated. Inform 



utli curve the 1 hybrids are also intermediate. The growth 

 curve at first rises rapidly, due in part perhaps to the good milk-giving 

 qualities of their vigorous F, hybrid mothers, but in part probably to 

 inheritance of cutleri qualities, since the cutleri growth curve is a rela- 

 tively steep but low one, indicating rapid growth at first and early 

 turity. The I hybrids also grow rapidly at first, being consider- 

 ably heavier than race B animals until an age of 120 to 150 days has 

 • ii reached. Then they fall below and stay below the weight of 

 race H animals, running a course nearly parallel with that of pure 

 cutleri animals, whereas the growth curve of the F x animals more nearly 

 approached that of race B animals. 



I -i Dayt 40 



\ ill curve - of nice R and cutlrri females and of their female hybrids, both Fi and Fj. 



\\ bile we are on this subject it may be well to refer to the growth 



curves observed in the cross between the Arequipa male, 1002, and 



females of race B (or of similar character). (See fig. 4.) The data for 



the growth curves of males are more complete in this case than the 



data for females and accordingly only the former will be considered. 



1 1 nimals are of greal size and vigor, attaining an average adult 



weighl of over 1,200 grams. The F 2 animals are even larger at birth 



than the I animals, a fact which indicates that the size of the mother 



mething to do, other than through heredity, with the size of the 



mg at birth, for the F a young rapidly lose the lead which they had 



in weight at birth over their F, parents, and subsequent to 40 days of 



fall below them in weight. At maturity they weigh less than 1,000 



having lost more than half of the gain which the F! animals 



showed over race B animals. This difference, it should be stated 



phatically, i- not due to environmental conditions of any sort, such 



