132 THE ORNITHOLOGIST. 



variety to the contents of its nest by depositing therein an egg 

 so dissimilar in most respects to the rest of the clutch that 

 unless one had actually seen it in situ and was acquainted 

 with its history, grave doubts might justifiably be entertained 

 concerning its propriety to belong to the clutch. And pretty 

 much the same may be said at times of the variety egg of the 

 Tree-Creeper. In some instances where there is no real or 

 fancied dissimilarity in the markings, the odd egg will be 

 found to differ in size, being larger or smaller as the case 

 may be. Last May, within the space of a few days, I 

 examined the nests of the following species, viz., Great 

 Titmouse, Blue Titmouse, Blackcap, Garden Warbler, Lesser 

 Whitethroat, Kestrel (an appropriated nest, of course), Yellow 

 Wagtail, Goldfinch and Willow- Wren, and, with the solitary 

 exception of the last-mentioned, what I have designated the 

 odd egg was present in each nest, represented either by a 

 difference in size or in colouring. Where this irregularity is 

 represented rather by size than by distinctive markings, it 

 will, I think, be generally found that the tendency of the odd 

 egg is to rather dwarf its fellows ; I mean that the remaining 

 eggs in the clutch will all be smaller than the variety type. 

 Nevertheless, having kept no actual statistics, I write subject 

 to correction, though I must confess that this seeming rule 

 has been honoured in the breach in two nests that I have 

 recently inspected, wherein, in the case of a Blackcap and 

 Lesser Whitethroat, the odd eggs were markedly smaller than 

 those amidst which they reposed. 



Now, that the broad fact is pretty much as I have stated 

 will, I think, be conceded by all who are conversant with the 

 subject, but can anyone establish a theory in explanation of it 

 that shall be so free from plausibility as to meet with popular 

 assent ? Certainly I have never come across any explanation 

 of a seeming, though by no means invariable, law of nature 

 that will stand the test of practical application, and for myself 

 I may state candidly that I neither hold one nor can I con- 

 ceive any absolutely reliable theory being put forward to 

 account for what appears to be much on a par with the 

 singular nesting economy of Cuculus canorus. Apparently 

 both are mysteries of nature for which no really satisfactory 

 explanation is forthcoming. 



