148 
NATURAL HISTORY OP 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 phalcence, 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 cuculus 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 i 
performing all the duties of incubation ; parasitism is extended over a considerable . 
number of species, and probably exists among most of the Cuculidce; 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 pf 
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 j 
its own, and there seems little cause to doubt that it lays several eggs at the usual i 
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. 
