MUTATION, FERTILITY, AND LONCKVITY IN INUICKD J.\l'\ i;i:il.l. UOVES. 



in their early plumages and 5 were abnormal abnormal in the direction of their 

 mutational male parent and the last 2 most decidedly like, tin ir "mutant" fatlur. 

 Further, the normal offspring arose from the earlier eggs of the season the first 

 5 and the seventh eggs producing the normals. The 5 mutants were from the 

 last 6 eggs permitting a decision, while the last 4 birds of the season were all 

 "mutational," the last pair most strikingly of all. The first "mutant," the 

 sixth egg from the last, was the least decisively mutational of all. Thus from 

 the first of the season to late season this series of offspring exhibited the 

 characters under examination in essentially the following order: normality, slightly 

 mutational, more mutational, most mutational. Photographs of 8 of these young, 

 the 5 mutants and 3 normals, are shown in pi. 7. All of these young, and the 

 parents as well, were photographed on the same day, September 29, 1912. 



It would seem, therefore: (1) that the male parent is a "true mutation," 

 having given the breeding test; (2) that early in the season the "mutation 

 recessive to the normal, but at the end of the season is dominant to the normal; 

 and (3) that a "graduated increase of dominance" is indicated by the lesser 

 amount of white in the earlier as compared with the greater amount of white 

 in the later offspring. 



The situation is, of course, not what one would expect on the basis of the muta- 

 tion theory and of Mendelism, but in such terms as are used under (1) and (2) 

 above it might be described, if one should feel obliged, even in the face of difficulties, 

 to cling still to "qualitative" interpretations of heredity phenomena. And, if 

 one had closed his note-book in September or October 1912 and were oblivious to 

 facts which deal with the history and longevity of offspring and of parents, and 

 with the "strength" of germs as affected by consanguinity, season, and overwork 

 at reproduction, one would have occasion to learn little of the nature and basis of 

 these phenomena of inheritance. 



With these latter data before us, however, we perceive that a truer description 

 of this inheritance embraces little of hypothetical factorial elaboration and symbol- 

 ism. When these two weak birds (the sire lived 30 months, the dam 28 month- 

 produced their strongest germs, known from other studies to he from the carlit r part 

 of the season, apparently normal (but weak and short-lived) offspring in r<- /*/Wo//. 

 The later, still weaker germs reproduced the striking abnormaKties of the "mutant" 

 father, and for the same general reason that these same abnormalities n-ere originally 

 produced in him, namely, that the level of developmental strength hay been lutnrul 

 the potency of the germ-plasm shifted. That, however, a special reason, namely, tin- 

 weak "mutant" condition of the father, is a prominent "explanatory" fcatui 

 the ready and consistent attainment of this weakened "mutant" condition of his 

 offspring, can not be doubted. In this male the general developmental power and 

 the specific power to produce certain parts of the color pattern were subnormal, 

 and under conditions which are otherwise known to reduce the developmental 

 level of germs the germs of this pair were easily, quickly, and consistently thrown 

 into the exhibition of a similar low level of developmental strength; and this low 

 level of color-pattern has, moreover, been found only in the immediate group to 

 which the father belonged and in his offspring. 



Moreover, a quite complete explanation of the situation involved here can not 

 be given without attention also to the later history of the mother of this group. 



