STATES OF INSECTS. (Egg.) 101 
rious larvee, small as it may be, must contribute some- 
thing to the hatching of the eggs deposited in them by 
various Ichneumons. In the fermenting bark in which 
the instinct of the rhinoceros beetles (Oryctes nasicornis 
&c.) impels them to place theirs, the dung which the Sca- 
rabeide select for that purpose, and the decaying vege- 
tables chosen by many other insects, a degree of artificial 
heat must exist: and the eggs, or rather egg-like pupe, 
of the spider-fly of the swallow (Craterina Hirundinis) 
are hatched by the heat of those birds which sit upon 
them along with their own eggs. 
Fabricius says, ‘* Insects never sit upon their eggs? ;” 
but certainly, as I formerly related to you», the female 
earwig does this, and one would be induced to suppose, 
from the circumstance of the young ones following their 
mother, as chickens do the hen, that Pentatoma grisea, 
formerly mentioned, may do the same °. 
With these exceptions, the eggs of all insects are 
hatched by atmospheric heat alone, the variations in 
which determine the more speedy or more tardy disclo- 
sure of the included insect. The eggs of such species as 
have several broods in the year, as the nettle butterfly 
(Vanessa Urtice), when laid in summer are hatched in a 
few days; but if not laid till the close of autumn, they 
remain dormant through the winter, and are only hatched 
at the return of spring. That this difference is to be at- 
tributed to the influence of heat has been often proved 
by experiment: the autumnal eggs if brought into a 
warm room may be hatched as soon as those laid in the 
height of summer. Silk-worms’ eggs naturally are not 
hatched till they have been laid six weeks, but in coun- 
* Philos. Ent. 76. > See above, Vor. I. 359—. © Tbid. 
