GUINEA-PIGS FROM AREQUIPA. 31 



HYBRIDIZATION EXPERIMENTS WITH A DOMESTICATED 



GUINEA-PIG FROM AREQUIPA. 



While in Arequipa, in December 1911, I purchased in the cabin of a 

 native living near the observatory a pair of domesticated guinea-pigs 

 about one-third grown and perhaps 2 or 3 months old. These animals 

 resembled the ordinary pied guinea-pigs kept for pets or laboratory use 

 in Europe and North America. The female was a tricolor, red, white, 

 and black, and was rough-coated of grade B (Castle, 1905, p. 57). The 

 male was a dilute-pigmented, agouti-marked tricolor (yellow agouti, 1 

 cream, and white), and smooth-coated. This pair of animals was suc- 

 cessfully transported to the Bussey Institution, where they produced 

 3 litters, of 1, 3, and 2 young respectively. The young of the first 

 2 litters died at birth; the third litter consisted of 2 males, and as 

 the mother died soon afterward it was impossible to propagate the 

 family farther for lack of females. Of the 6 young produced, 3 were 

 rough-coated and 3 smooth, showing the mother to have been hetero- 

 zygous for rough coat, a dominant character (Castle, 1905). Three 

 were golden agouti and white and three tricolor, one being golden 

 agouti red and white, the other two silver agouti yellow and white. 



MALE 1002 AND HIS F x OFFSPRING. 



The father of this family of guinea-pigs (of 1002) proved to be an 

 animal of great vigor and vitality. Although born in Peru (about 

 September 1911) and brought to North America in mid-winter, he has 

 successfully escaped the ravages of disease among our guinea-pigs 

 throughout the rigors of four New England winters and is still vigorous 

 and active. In crosses with other races of guinea-pigs he has sired 

 several hundred young and is now being mated with females which are 

 simultaneously his daughters, his granddaughters, and his great- 

 granddaughters! By repeated back-crosses such as these a race has 

 been established which derives its inherited characters largely from 

 this one animal. This race will be designated the "Arequipa" race. 



Crosses of 0*1002 and repeated back-crosses with his female descen- 

 dants have permitted a very full analysis of the factorial constitution 

 of this animal. He possesses either as dominant or as recessive char- 

 acters a majority of the Mendelian variations of guinea-pigs, including 

 one not previously known to occur in any animal other than mice, viz, 



x It should he noted that "silver agoutis" may he of two different sorts: (1) dark-eyed silver 

 agouti with cream-colored hair-tips, and (2) red-eyed silver agouti with white hair-tips. The two 

 varieties resemble each other somewhat and it often requires close observation to discriminate 

 between them, but genetically they are quite distinct. Only the former sort was known to me 

 previous to the Peruvian expedition, and the term "silver agouti" as used in my 1905 paper and 

 by fanciers generally refers to this. It would be better, I think, to use the term cream agouti or 

 yellow agouti for such agouti animals as develop pale yellow in the fur and to restrict the term 

 silver agouti to those which are non-yellow. 



