550 Mr. C. F. M. Swynnerton on 



2. Diversity and Distinctiveness, also the Tendency^ to 

 Uniformity within the Species or Form. — Should it be found 

 not meiely that nauseousness exists, but that there is a 

 gradation between some species of eggs that are only eaten 

 through hunger aud others that an individual enemy -will 

 eat to repletion-point, we may conclude that the need for 

 distinguishability from pleasanter forms (parent and other- 

 wise) is, and has been, widespread, and we shall have at least 

 a contributory explanation for the qualities italicised above. 

 Probably, in many cases, somewhat more than a merely 

 contributory explanation — for inter-recoguition between 

 eggs is out of tlie question, and necessity for recognition by 

 parents is probably urgent only in those species (numerous 

 enough) that may be victimized by Cuckoos, though just 

 possibly preseut (as Mr. G. L. Bates suggests) in birds that 

 build in close colonies, where, however, it would encourage 

 variability. 



The necessity for differentiation from less deterrent parent- 

 forms might well have been of much importance, for, unac- 

 companied by some distinguishing mark, a variation in the 

 direction of greater nauseousness is unlikely to be actually 

 selected. The selection of the curiously netted chalk layer 

 in the egg of the Guira Cuckoo aud of much else that is 

 striking and peculiar in eggs (and in animals generally) 

 could be in part accounted for in this way ; while the 

 oft-repeated necessity for differentiation from successive 

 parent-forms that might accompany a very gradual or much 

 interrupted increase in indigestibility might conceivably 

 sometimes produce the utmost heights of distinctiveness. 

 Whether such variability as we find in the eggs of the 

 Guillemot will be explained as due merely to the absence 

 of the necessity for recognition by enemies (whether through 

 present high acceptability or the fact that an enormous 

 annual colony and the qualities of its eggs, irrespective of 

 coloration, will be a matter of the utmost notoriety to the 



• I use the word advisedly, for such a " tendency " actually exists, in 

 spite of the great variability of many eggs — a variability that I believe 

 to be perfectly explicable. 



