188 GENETICS AND EUGENICS 



three as in rabbits. They are (a) ordinary pigmentation, 

 (6) ruby-eyed dilution (Whiting) — perhaps homologous with 

 red-eyed dilution in guinea-pigs — and (c) albinism. 



In Drosophila a factor for eye-color has been discovered 

 in several allelomorphic forms, such as white, eosin, buff, 

 cherry, blood, and red, analogous with the allelomorphs of 

 the color factor found in guinea-pigs. 



The agouti factor of rodents occurs in the rabbit in three 

 allelomorphic forms, (a) ordinary gray, (6) black-and-tan, 

 and (c) non-agouti. In mice the agouti series includes (a) or- 

 dinary gray, (b) gray with white belly, (c) yellow, and {d) 

 non-agouti. In a cavy {Cavia rufescens) and its guinea-pig 

 hybrids, it has three forms, (a) agouti with hght belly, 



(b) agouti with ticked belly, and (c) non-agouti. 



The extension factor has in rabbits three allelomorphic 

 forms (a) ordinary extension as in gray or black rabbits, 

 (6) "darkened" extension (DE, Punnett) seen in steel gray 

 rabbits, and (c) non-extension (restriction) seen in yellow 

 and in tortoise rabbits. Extension in guinea-pigs assumes 

 three alternative forms seen in (a) black, (6) tortoise, and 



(c) yellow. 



White spotting shows numerous allelomorphic forms. In 

 rats (a) hooded pattern, (6) "Irish" pattern, and (c) self 

 pattern are allelomorphs. In rabbits, all known forms of 

 white spotting behave as allelomorphs. These include at 

 least three different patterns of Dutch marking as well as 

 English markmg.^ 



In silkworms Tanaka discovered a series of three factors 

 for marking of the larva, which behave as allelomorphs, 

 although he prefers to describe them as factors completely 

 coupled. The three are Q (quail), Qs (striped quail) and Qm 

 (moricaud quail). He also observed several minor forms of 

 Q, which he designated QS Q^, Q^, and Q*, which consider- 

 ably extend the allelomorphic series, but which differ so 



' But in mice two forms of white spotting are known which are not allelomorphic, 

 nor even linked. These are known as black-eyed white and piebald respectively. 

 On the chromosome theory, they must be located in different chromosomes. 



