168 ORTHOGENETIC EVOLUTION IN PIGEONS. 



of breaking up the dark center into lateral, gradually disappearing chequers. The 

 present section is concerned with another aspect of this same "guinea-mark" which 

 in 1906 came under observation, as a mutation, in a single individual of the species 

 Zenaida vinaceo-rufa Ridgway. This genus and the other genera of Zcnaidinse 25 

 have passed beyond the phylogenetic stage which is represented by the "guinea- 

 mark," Nesopelia not far beyond it; but in Zenaida and Zenaidura even most of 

 the chequers which arose from the later extensions of the mark have been obliterated, 

 while in Melopclia only a few structural imprints of obsolete chequers remain. 



It is only with the aid of this phylogenetic perspective that the total behavior 

 of the Zenaida mutation can be understood. But, because this perspective is avail- 

 able, and because some of the special conditions which attended the origin of the 

 individual bearing the mutational character are known, this mutation contributes 

 perhaps more to our knowledge of the phenomenon of mutation than does any 

 mutant, or group of mutants, hitherto recorded. 



The further important facts concerning this mutation, as they may be stated 

 in a preliminary or introductory fashion, are as follows: (1) The mutational char- 

 acter is not a really new thing; a very weak stage (a smaller area affected, and 

 usually of buff color, not white) is often seen in some restricted regions of the body 

 in young zenaidas and in many other forms; (2) the mutational character is exhibited 

 only in the juvenal plumage; representing, as it does, delayed or halted development, 

 it attains in kder plumages the normal state of the species; (3) the author's knowl- 

 edge of the place of this character in pigeon phylogeny enabled him to predict its 

 disappearance in these later plumages; (4) the original mutant arose from a germ 

 which, from other and previous studies, could be identified as a "weakened germ"; 

 (5) the mutation has now been perpetuated — undiminished — into the fifth genera- 

 tion, in a generic cross. 



The author did not prepare these data for publication. Fortunately, however, 

 he made fairly complete notes concerning the essential aspects of the mutation, 

 and recorded his views and conclusions with sufficient fullness to permit a fairly 

 adequate presentation of the subject. The editor chooses the following topical 

 arrangement of materials, because more of the author's statements may thus be 

 utilized with least change or transposition. The breeding of the later generations 

 of this mutation has been continued (early 1911 to 1916) by the editor. The 

 author's data on the breeding of the mutant, and of her offspring, have been tabu- 

 lated and presented in full in Chapter X, Volume II. The mutant was not bred to 

 one of her own kind, but with a mourning-dove {Zenaidura) ; this makes necessary 

 the author's description of the normal young of both of these species. 



On the Color of the Yodng of Zenaida and Zenaiduha. 



In making a comparison of the juvenile color of Zenaida vinaceo-rufa and Zenai- 

 dura carolinensis I have before me one of each kind about 2 weeks old (June 7, 

 1905). The Zenaida (No. 12 = mother of the original mutant, No. 21. — Ed.) has 

 more of the red color of the turtle-dove. Both species have two light streaks on 

 the side of the head, one running over the eye (superciliary), the other below it, 

 and running through the ear-coverts (auricular). The feathers in these streaks 

 have the 'light edge' (which is characteristic of the entire. body-surface — head, neck, 



26 See Chapter V of this volume. 



