CONTENTS. 



Part I. — An Expedition to the Home of the Guinea-pig and Some Breeding 

 Experiments with Material there Obtained. Bt W. E. Castle. 



page. 



Introduction 3 



Some observations on guinea-pigs in Peru 5 



Hybridization experiments with Cavia cutleri 8 



Life history of C. cutleri 8 



Crosses of C. cutleri males with guinea-pig females 13 



Color inheritance among the F 2 hybrids 13 



(a) Cross 9 albino (race B) X d" C. cutleri 13 



(6) Cross 9 albino (race C) X cf C. cutleri 14 



(c) Cross 9 brown-eyed cream (race C) X cf C. cutleri 16 



(d) Results from (b) and (c) combined 16 



(e) Intensity and dilution among the hybrids 17 



(/) Significance of the results observed 18 



Hybridization experiments with a race of feral guinea-pigs from lea, Peru 20 



Origin and characteristics of the lea race 20 



Crosses between the lea race and guinea-pigs of race C 23 



The F 2 generation 24 



Summary on the lea race 29 



Hybridization experiments with a domesticated guinea-pig from Arequipa 31 



d 1 1002 and his Fi offspring 31 



F 2 offspring of d" 1002 33 



Back-cross and other offspring of d 1 1002 35 



Miscellaneous matings of the descendants of cf 1002 36 



Summary on the Arequipa domesticated race 41 



Size inheritance in guinea-pig crosses 42 



Previous work on size inheritance 42 



Weights and growth curves of C. cutleri, of various guinea-pig races, and of their 



hybrids 43 



Skeletal measurements of C. cutleri, of various races of guinea-pigs, and of their 



hybrids 47 



The C. cutleri hybrids 48 



Hybrids of the Arequipa d 1 1002 52 



The lea hybrids 53 



Theoretical explanations of size inheritance and of "blending inheritance" 



in general 54 



Part II. — An Intensive Study of the Inheritance of Color and of Other Coat 



Characters in Guinea-pigs, with Especial Reference to Graded Variations. 



By Sewall Wright. 



page. 



Color and its inheritance in guinea-pigs 59 



Skin, fur, and eye colors of guinea-pigs 59 



Color of Cavia cutleri 59 



Melanin pigment 59 



Primary classification of fur colors 59 



Yellow group of colors 



Dark group of colors "0 



Skin colors "1 



Eye colors "2 



Definitions of fur colors by Ridgway's charts 62 



Definitions of eye colors 



Heredity of fur and eye color 



Color factors of guinea-pigs 63 



Classification of color factors 63 



iii 



