172 ORTHOGENETIC EVOLUTION IN PIGEONS. 



and of similar pale-brown color, in some Japanese and European turtle-doves, in 

 the young of Leptoptila, and in the young of Florida ground-doves. 38 



This character (white guinea-mark) is a permanent character in the guinea- 

 pigeon of Africa. In this species we should have no doubt about calling it a charac- 

 ter. The mutationist would hold that it was an "immutable unit." Yet we see 

 that it certainly is only an enlargement of the very minute dividing-line. Even in 

 this specimen it is reduced to mere lines on the crown of the head and on the throat. 

 What appears then to be a mutation turns out to be not a really new thing, but an 

 extension and intensification of the normal mark. 



Is there any explanation for this? I can account for it only by referring it to 

 the hard time the bird passed during the first 2 or 3 days of its life. The old birds 

 seemed to me to be a little unsteady about the time the egg was due to hatch. I 

 decided therefore to place the egg under a pair of white rings which had a young 

 nearly 2 days old. The egg hatched and the young was strong and tried hard to 

 get food from the foster-parents; but they did not feed it. I held it up and gave it 

 every chance, but they still refused to feed it, although they kept on feeding their 

 own young, which was larger and stronger. I left it for a whole day to them and 

 then placed it under another pair. The latter had an egg due to hatch, and the 

 male fed the zenaida a little. After a few hours I again returned it to the white 

 rings, taking away from them their own young, thinking that by the next morning 

 they would feed. They sat on the nest, but refused to feed. When the zenaida 

 was fully 2 days old I tried it under another pair that had eggs due to hatch. These 

 birds fortunately fed the zenaida, and it grew rapidly, as these foster-parents were 

 comparatively large birds. The zenaida flourished henceforth with plenty of food. 

 It may be that the lack of food for the first two days was the cause of this enlarged 

 mark a sort of albinism. 39 



The editor should at this point call attention to the fact that the preceding 

 account was written, as noted above, when this bird was but 6 weeks old and before 

 a breeding-test of the mutation had been made. At the time this was written the 

 author well knew that lack of food, tuberculosis, etc., were able to produce feathers 

 with a reduced pigmentation, or even to suppress it altogether (albinism). 39 



In a note written two years later (in 1908) the author wrote: "This mutant 

 (21) hatched September 28, 1906, from the second egg of the clutch"; underscoring 

 the words "September" and "second." In view of the other data then at hand 

 on the relation which both season and the order of the eggs of the clutch bear to the 

 weakness of germs, it seems certain that these points were then in his mind as the 

 chief explanatory features of the appearance of this mutation. 



It has already been noted that the breeding data for the offspring of the mutant 

 (21) are fully given in Volume II. The results in the first generation are, however, 

 also given here in table 7. This table should prove of assistance in an examination 

 of the illustrations of the subject, these illustrations being confined to this volume. 



The offspring of several generations to 1916 are shown in plates 85 and 86. 

 The figures of these plates and the tabulated breeding data show, among other facts, 



The young of Zenaida auriculaia, according to Salvadori (Catalogue of Birds, Brit. Mus., Vol. XXI, p. 386), 

 'have feathers of the upper parts and breast with white mesial streaks and edges; the primaries and primary-coverts 

 Oged with rufous." 



' Soc Volume II, particularly Chapter XIV. It will (later) be seen that the author later recognized after a breed- 

 ing-test that the cause of the variation or mutation was terminal, not environmental. ED. 



