670 



THE AMEBIC AN NATURALIST 



[Vol. L 



The element added in this last cross is plainly the brown 

 gamete carried by the black. This brown gamete, how- 

 ever, has received something additional from the black- 

 and-tan race, so that when red unites with this changed 

 brown gamete the result is a darkening and intensification 

 of the brown pigments to produce a brown-and-tan or 

 brown-sable, a process quite parallel to that which pro- 

 duces black-and-tan and black-sable in the pure black X 

 red cross. 



A few crosses were made between pure-bred black-and- 

 tan and brown, and although the numbers here are small, 

 the indication is that the result will be the same as in the 

 black X red cross. F x consisted of blacks and black- 

 sables ; the sables when back-crossed to browns gave ap- 

 proximately equal numbers of blacks (26) and browns 

 (20) and also the two yellow series as follows: 



Black sables (mean grade 3.5) . . 11 Brown sables (mean grade 4) . . . 10 



fellows and sooties 3 Beds and yellows 10 



Total 14 Total 20 



This back-cross with the recessive brown gives a direct 

 index of the yellow gametes of the Fj sables. That they 

 vary in darkness should be borne in mind during the dis- 

 cussion of the difference between black-and-tan and 

 yellow. 



The reds in suitable crosses showed the same tendency 

 to produce fluctuating blends. Mated with creams they 

 gave yellows of an intermediate shade (16) and recessive 

 non-yellows (10). These light reds were bred inter se 

 and tested by crossing with browns. The young (100 in 

 number) fluctuated in intensity about the shade of the 

 light red parent or parents. Full intensity was not recov- 

 ered except in back-crosses. Hence red is likewise a form 

 of yellow, differing from it by an added intensity which 

 blends in crosses. 



The foregoing evidence has merely pointed to the yel- 

 low nature of black-and-tan and red ; has classified them 

 and their derivatives among the yellows, and has hinted 



