Habits of the Cuckoo. 291 



after it is matured, till it has discovered a nest in a fit state 

 to deposit it in." (Rennie's Mont. Orn. Diet., art. Eggs of 

 Birds, p. 163.) Our correspondent, Mr. Hoy, seems (V. 

 278.) favourable to this opinion, and has mentioned a fact in 

 support of it. Montagu has adduced the following infer- 

 ence in connection with his opinion quoted above. " The 

 consequence of this retention would be a dilatation of the 

 embryo, by the internal heat of the body (the viper is ovi- 

 parous, or, rather, ovo-viviparous, hatching its young by the 

 internal heat of its body), and the fcetus advanced towards 

 perfection in proportion to the time the egg remained in that 

 state. Of course, after such a previous enlargement of the 

 fcetus, were the egg dropped into the nest of a bird on the 

 point of sitting, it would most certainly be hatched as long be- 

 fore the eggs of the bird whose nest it was deposited in as it 

 had been forwarded in the uterus. It has frequently been 

 observed, that, where the egg of a cuckoo has been found in 

 the nest of a bird together with some of its own, that the 

 cuckoo's egg is hatched first. (Jenner, Nat. Hist, of the 

 Cuckoo, p. 3.) [See VIII. 287.] This seems difficult to ac- 

 count for, unless upon the principle we have suggested, as 

 the egg of that bird is rather superior in size to that of any 

 bird whose nest it makes choice of to deposit it in ; amongst 

 which the yellow hammer's is the largest, weighing, in general, 

 from 36grs. to 46grs.; whereas that of the cuckoo weighs 

 from 44grs. to 54grs. The other birds which the cuckoo 

 more generally chooses to incubate its eggs, seldom produce 

 eggs above 40grs. in weight, and mostly from 30grs. to 

 36 grs. ; if, therefore, the embryo of the cuckoo were not 

 sometimes enlarged before the egg was laid, is it reasonable 

 to suppose it would be first hatched?" We hope that our 

 presentment of these views will induce correspondents to 

 communicate a statement of any facts which may tend to test 

 the truth of them. 



Montagu has stated, in the same article on the Eggs of 

 Birds, that, " By experiment, it appears, that birds do not 

 instinctively know the necessary time of incubation ; for we 

 have repeatedly taken the eggs of a bird unincubated, and 

 placed them under another of the same species, who was on 

 the point of hatching, and, vice versa, those on the point of 

 hatching into the nest of such as had only begun to sit; and 

 in both cases the young were brought to maturity." The 

 import of this statement does not oppose Montagu's conjec- 

 ture, that the cuckoo's egg may be partly hatched before it is 

 layed, for he has not stated that the young which had been 

 c< brought to maturity," that is, hatched and reared, from the 



