THE MUTATION THEORY AND MUTATIONS. 167 



offspring (MN 1). In 1913 reduced available breeding-space prevented attempts 

 to mate this bird. The results for 1914 are included in table 5. The results then 

 obtained indicate much weakness on the part of one or of both of these parents. 



It remains to consider the question whether the mutational character of the 

 original guinea mutant (20) can be attributed to "weakness" of the germ from 

 which it arose. The author has recorded no statement whatever on this point. 19 

 But all of the color mutations recorded by the author depart from the normal in 

 the direction of lighter (or white) color; and he has elsewhere pointed out that 

 "the direction of evolution" in the pigeon world is also toward light (or white) 

 color. In the case of each of the three color mutations which he did more fully 

 describe, he has pointed to weakness — in the parents, or sometimes more specifically 

 to the weakness of particular germs from which the mutant arose — as the basis 

 of the mutation. These several facts make it seem quite probable that the author 

 would have discussed this mutation from a similar standpoint. 



The several conditions which tend toward the production of weakened offspring 

 or of weakened germs need receive but little attention here, since they are fully 

 treated elsewhere. 20 It may be said at once, however, that the breeding-record 

 given (for this purpose) in table 4 apparently does not wholly accord with the view 

 that mutant No. 20 arose from a "weak" germ. For example, the mutant lived 

 longer, perhaps, than did any of its brothers or sisters. 21 Again, it is not evident that 

 the other eggs of the same period — laid immediately before and after the mutant- 

 producing egg — were producing females predominantly. 22 On the other hand, the 

 following can be said: The data of the table are not very complete; the mutant 

 arose from one of a series that was being produced with abnormal rapidity, and was 

 the eighteenth of such a series; only one later clutch was laid before the parents 

 began their season of rest — freedom from egg-production — and the length of life 

 of the fraternity probably indicates weakness throughout the fraternity. A further 

 and unquestionable expression of weakness in this fraternity is given in the breeding- 

 record of two or (probably) three of its members. The result, as seen in table 5, 

 shows extraordinary developmental weakness, and the two offspring which here 

 lived long enough to develop plumage characters both shared the mutational char- 

 acters of their sire. 



THE ZENAIDA MUTATION. 23 



In the preceding section the "guinea-mark" was the point of departure for a 

 mutation. That mutation took the direction which the author had concluded from 

 other studies 24 was the direction of evolution in the Columbae. The mark itself 

 represents an extension of the pale apical edge — considered universal in pigeons 

 either as a permanent {e.g., Turtur orientalis) or as a recapitulated (e.g., Zenaida, 

 Geopelia) character; and the further extension of this particular mark is the means 



19 There are, however, the best of reasons for this omission. First, offspring from this mutation were obtained 

 only a few weeks before the author's final illness; and, second, other unfortunate affairs quite precluded this sort of 

 work during the 5 or months which preceded his brief and fatal illness. — Ed. 



20 Vol. II of these works; also see under "the Zenaida Mutation," the next topic in this chapter. — Ed. 



21 It is conceivable, but rather doubtful, that because of its value it received much better care than other members 

 of the fraternity. — Ed. 



22 The author considered this an evidence of weak germs; my own experience fully confirms this view. — Ed. 



23 Three mutations — all similar — in the Japanese turtle-dove (Turtur orientalis) are fully described in Volume II, 

 Chapter V. 



24 See the preceding chapters of this volume. 

 12 



