No. 62.5] PIXK-EYED SELE WIUTK GUIXEA PlG^ 129 



sion factor {E) which extends the bhick. The presence 

 of these two factors tends to make the extremities heav- 

 ily pigmented. 



The albino guinea-pig, according to llic fmiciors' 

 standard, should be as completely wliito ns the nlhiiios 

 of other species. This, however, has never been entirely 

 attained, even though much selection has been practised. 

 Albinos most nearly approaching the standard lack both 

 black and extension factor and are therefore eh. When 

 mature they ordinarily show, nevertheless, a lightly pig- 

 mented rim along the edges of the ears. The synthetic 

 pink-eyed whites, produced as explained in the earlier 

 part of this paper, are, on the other hand, pure white, 

 and they tlierefore satisfy the fanciers' standard in this 

 respect. They would meet his desires, furthermore, in 

 that they l)reed true for this character. 



There are other means besides those already men- 

 tioned whereby pink-eyed self white guinea-pigs could be 

 produced w^hich would satisfy the fancier's standard. 

 One method would be to combine a self white condition 

 described by Castle (1905) witli the ]nnk-eyed. Self 

 whites of this type, however, do not bn-ed true. A'ery 

 frequently they throw^ spotted ori'sru iuu-. Tliey se.^m to 

 be merely an extreme form of white spotting, all of the 

 animal being unpigmented except the eyes. Pink-eyed 

 self-whites of this type would necessarily on this ac- 

 count be very unstable in the transmission of their coat 

 character. 



Another method would be to prodijce a pink-eyed " 

 ipp) albino. The pink-eyed factor in this case would 

 cause the pigmentation ordinarily found in albinos to 

 become invisibh\ "\Ve have produced an animal of this 

 type. AVlien mated to ])iiik-eye(l it had uotliing Imt pink- 

 eyed ()ffs))i-iiig, and wlieti mated to a]l)iiios it had only 

 al])ino offspriiig. It was |)ni-e whiti" in color. 



It seems quite proliabh- that synthetic pink-ey.-d s.^lf 

 whites may also be ])rodueed in rats. Casth' ( r.>14) lias 

 already described yellow varieties and piidv-eyed varie- 



