148 NATURAL HISTORY OF SELBORNE. 



because, if their formation proves the same, the reason for incapacity 

 in the cuckoo will be allowed to have been taken up somewhat hastily. 



Not long after a fern-owl was procured, which, from its habit and 

 shape, we suspected might resemble the cuckoo in its internal con- 

 struction. Nor were our suspicions ill-grounded; for, upon the 

 dissection, the crop, or craw, also lay behind the sternum, immediately 

 on the viscera, between them and the skin of the belly. It was bulky, 

 and stuffed hard with large phcdcence, moths of several sorts, and their 

 eggs, which no doubt had been forced out of those insects by the action 

 of swallowing. 



Now as it appears that this bird, which is so well known to practise 

 incubation, is formed in a similar manner with cuckoos, Monsieur 

 Herissant's conjecture, that cuckoos are incapable of incubation from 

 the disposition of their intestines, seems to fall to the ground ; and we 

 are still at a loss for the cause of that strange and singular peculiarity 

 in the instance of the cuculiis canorus* 



We found the case to be the same with the ring-tail hawk, in respect 

 to formation ; and, as far as I can recollect, with the swift ; and probably 

 it is so with many more sorts of birds that are not granivorous. 



I am, &c. 



LETTEE XXXI. 



TO THE SAME. 



SELBORNE, April 29th, 1776. 



DEAR SIR, On August the 4th, 1775, we surprised a large viper, 

 which seemed very heavy and bloated, as it lay in the grass basking in 

 the sun. When we came to cut it up, we found that the abdomen was 

 crowded with young, fifteen in number ; the shortest of which measured 

 full seven inches, and were about the size of full-grown earth-worms. 

 This little fry issued into the world with the true viper-spirit about 

 them, showing great alertness as soon as disengaged from the belly of 

 the dam : they twisted, and wriggled about, and set themselves up, and 

 gaped very wide when touched with a stick, showing manifest tokens 

 of menace and defiance, though as yet they had no manner of fangs 

 that we could find, even with the help of our glasses. 



* There is nothing in the anatomical structure of the cuckoo to prevent its 

 performing all the duties of incubation ; parasitism is extended over a considerable 

 number of species, and probably exists among most of the Cuculidc? ; a large 

 black species, Eudynamys orientalis, has had its habits detailed by Mr. Blyth, 

 in " Contributions to Ornithology for 1850." It selects a species of crow generally 

 for the foster-mother, and it is a remarkable instance of design that the eggs of 

 both birds are nearly similar in colour, that of the cuckoo being rather smaller in 

 size. It is suspected that this species breaks the eggs of the crow before depositing 

 its own, and there seems little cause to doubt that it lays several eggs at the usual 

 periods, the same as other birds. The genus Dolyconyx, among the Icterine birds, 

 also breeds parasitically, while several species of birds depute the office of incu- 

 bation to artificial heat, of which the most remarkable is the hotbed-making 

 Megapodius of Australia. There is another form which this habit assumes, com- 

 monality of hatching, as in Crotophaga, where various individuals make use of a 

 common nest and hatch by turns. The whole subject is very curious, but 

 there is a difficulty in procuring exact details of the habits of foreign species. 



