14 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



ROAN, AND SILVERED. 



In roan animals white hairs are interspersed with red ones. A simi- 

 lar modification may occur in the coat of black animals also, which are 

 then said to be " silvered." I have never seen a cavy with an entire 

 coat of this character ; usually certain patches only are affected, or 

 more often the ventral part only of a patch. I have noticed, however, 

 the transmission of this character from generation to generation and 

 have no doubt that a roan race or a silvered one could be established 

 if desired. 



RESULTS OF CROSSING THE ELEMENTARY COLOR VARIETIES. 

 ALBINOS AND PIGMENTED ANIMALS.* 



These two types are very distinct. Each by itself breeds true, and 

 cross-breeding between them fails to produce intermediates ; it results 

 invariably in the production of young of the centripetally pigmented 

 type. Thus in the course of these experiments, (i) albino parents 

 mated inter se have produced 156 young, all albinos; (2) pure pig- 

 mented parents (/. ., animals altogether devoid of the albino charac- 

 ter) mated inter sc have produced 261 young, all pigmented; and (3) 

 albinos mated to pure pigmented animals have produced 314 young, 

 all pigmented. The young produced by this last sort of mating, 

 though similar in appearance to those produced by (2), are not pure 

 pigmented animals, for they possess the potentiality to form albino 

 young, which the young of the two pure pigmented parents do not. 

 In Mendelianf terminology the pigmented character is dominant, the 

 albino character is recessive, and cross-breds between a dominant and 

 a recessive parent are hybrid dominants. The hybrids form gametes 

 (I. e., spermatazoa and eggs ready for fertilization), half of which, ap- 

 proximately, transmit the pigmented character, half the albino character. 



Students of heredity at the present time are giving earnest attention 

 to testing the two principles which make up Mendel's law, viz, (i) 

 the principle of dominance, and (2) the principle of segregation. In 

 the case under consideration there can be no question of the validity of 

 both. The centripetal type of pigmentation invariably dominates over the 

 albino, as the statistics already given clearly indicate. This is in harmony 

 with numerous observations on mice, rats, rabbits, and other mammals 

 made by Haacke ('95), Von Guaita ('98,100), Cuenot (103,: 04), 



* Although, as we have seen, the albino guinea-pig regularly develops a cer- 

 tain amount of pigment in its coat, it will be convenient to use the term 

 "albino" in contrast to "pigmented," the latter term referring only to the 

 dark-eyed centripetally pigmented animals. 



t For a brief statement of Mendel's law, see Castle ( : 03, or : 031) ; for a fuller 

 one see Bateson (: 02). 



