VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 43^ 



sat on a few days, and had them immediately conveyed to the spot, and placed 

 under the cuckoo. On the Qth day after the eggs had been in this situation, 

 the person appointed to superintend the nest, as it was some distance from the 

 place of my residence, came to inform me, that the wagtails were hatched. On 

 going to the place, and examining the nest, I found nothing in it but the 

 cuckoo and the shells of the wagtail's eggs. The fact therefore of the birds 

 being hatched, I do not give as coming immediately under my own eye ; but the 

 testimony of the person appointed to watch the nest was corroborated by that of 

 another witness. 



To what cause then may we attribute the singularities of the cuckoo ? May 

 they not be owing to the following circumstances ? The short residence this 

 bird is allowed to make in the country where it is destined to propagate its spe- 

 cies, and the call that nature has on it, during that short residence, to produce 

 a numerous progeny. The cuckoo's first appearance here is about the middle of 

 April, commonly on the 17th. Its egg is not ready for incubation till some 

 weeks after its arrival, seldom before the middle of May. A fortnight is taken 

 up by the sitting bird in hatching the egg. The young bird generally continues 

 3 weeks in the nest before it flies, and the foster-parents feed it more than 5 

 weeks after this period ; so that, if a cuckoo should be ready with an egg much 

 sooner than the time pointed out, not a single nestling, even one of the earliest, 

 would be fit to provide for itself before its parent would be instinctively directed 

 to seek a new residence, and be thus compelled to abandon its young one ; for 

 old cuckoos take their final leave of this country the first week in July. 



Had nature allowed the cuckoo to have staid here as long as some other 

 migrating birds, which produce a single set of young ones, as the swift or night- 

 ingale for example, and had allowed her to have reared as large a number as any 

 bird is capable of bringing up at one time, these might not have been sufficient 

 to have answered her purpose ; but by sending the cuckoo from one nest to ano- 

 ther, she is reduced to the same state as the bird whose nest we daily rob of an 

 egg, in which case the stimulus for incubation is suspended. Of this we have a 

 familiar example in the common domestic fowl. That the cuckoo actually lays 

 a great number of eggs, dissection seems to prove very decisively. On a com- 

 parison T had an opportunity of making between the ovarium, or racemus vitel- 

 lorum, of a female cuckoo, killed just as she had begun to lay, and of a pullet 

 killed in the same state, no essential difference appeared. The uterus of each 

 contained an egg perfectly formed, and ready for exclusion ; and the ovarium ex- 

 hibited a large cluster of eggs gradually advanced from a very diminutive size, to 

 the greatest the yolk acquires before it is received into the oviduct. The appear- 

 ance of one killed on the 3d of July was very different : in this I could distinctly 

 trace a great number of the membranes which had discharged yolks into the 



