394 CUCULID.E. 



events. There is abundant proof that the time of its inser- 

 tion is very variable. It may be deposited before the owner 

 of the nest has laid any egg of her own, or after she has 

 completed her clutch. Several authorities have declared that 

 the Cuckow's egg needs not so long a period of incubation 

 as the eggs of most of the birds upon which its care is 

 imposed ; but this is a matter that must at present be 

 deemed undecided.* In due time it is hatched, and then 

 takes place one of the most wonderful things in the whole 

 history of this wonderful bird ; for the discovery of which we 

 are indebted to the accurate observations of the celebrated 

 Edward Jenner, as related by him in a letter to John Hunter, 

 by whom they were communicated to the Royal Society 

 (Phil. Trans. 1788, pp. 219-237). So strange a chapter of 

 Natural History had never before been published, and it is 

 by no means surprising that some of the contemporaries of 

 those great men hesitated to credit what they therein read. 

 Jenner's account of what he saw has, however, been fully 

 confirmed by later experience, and exception can only be 

 taken to some minor details of which it was impossible for 

 him to assure himself. f It had of course been commonly 

 known for centuries that very soon after the Cuckow was 



having been found in the nests of the following species though not necessarily 

 in the British Islands : all the Shrikes; the Spotted Flycatcher ; the Golden 

 Oriole ; the Song-Thrush, Mistletoe-Thrush (Zool. Garten, 1878, p. 177), Black- 

 bird, Ring-Ouzel and Rock -Thrush ; the Sylviidce except the Rufous, Savi's and 

 the Yellow-browed Warbler ; the Wren ; the Treecreeper ; the Great Tit- 

 mouse ; all the Wagtails and Pipits ; the Larks except the Shore- and the White- 

 winged Lark ; the Reed-, Great, Yellow and Girl -Bunting and the Ortolan ; 

 the Chaffinch and Brambling, the Tree- and House-Sparrow, the Hawfinch 

 and Greenfinch, the Serin, the Linnet and Mealy Redpoll and the Bullfinch ; 

 the Swallow; the Daw, Pie and Jay ; the Ring-, Stock- and Turtle-Dove ; and, 

 most strange of all, the Little Grebe (Journ. fur Ornith. 1876, p. 391) ! But 

 of these birds, seventy-eight in number, four the Hedge-Sparrow, Reed- 

 Warbler, Pied Wagtail and Meadow-Pipit, deserve particular notice as being 

 those most commonly chosen as foster-parents. 



* Thus Jenner, in the course of his observations immediately to be mentioned, 

 thought that the Cuckow's egg is usually hatched first, but he knew of one 

 instance to the contrary (p. 228, note). 



f For instance where he states (p. 221) that the Cuckow's dupe "whilst she is 

 sitting, not unfrequently throws out some of her own eggs, and sometimes 

 injures them in such a way that they become addle." 



