6o Life History of Coimnon Cuckoo. 



about hereditary influence on cuckoo's eggs, said : — 

 " I do not see why the presumed habit should be 

 more likely to be hereditary in the cuckoo than in 

 any other species. Mr. Newton, it is true cites an 

 instance or two of there having been a family likeness 

 found between the eggs laid by the same bird, so that 

 they could be readily distinguished from others ; but 

 these rare — not to say accidental — varieties in the col- 

 ouring of eggs may arise from different causes — for 

 instance, the age of the bird or defective organization. 

 The eggs of many birds are found to vary more or 

 less in colour, — the eggs of the common house- 

 sparrow, for instance, — though I know of no regular 

 or permanent varieties in the species.'' 



And, let Professor Newton now reconcile it how 

 he may, we are fully assured that, in this last sen- 

 tence, Mr. Hadfield, from his point of view, is right. 



VI. 



The peculiar formation in the cuckoo which is said 

 to prevent incubation is shared in greater or lesser 

 degree with other birds which do incubate. This 

 malformation results from the stomach lying beneath 

 the sternum ; but the nightjar is so formed, and yet 

 it broods its own young ; and more recent investi- 

 gators show that at least one other brooding bird has 

 the same form ; while the two common North Ameri- 

 can cuckoos have the same form, and yet brood some 

 of their eggs and young ones. The cause of the 

 habit must therefore be sought in other sources. 

 Herissant attributed the non - brooding of the 



