ENTOMOLOGY. 
75 
of the shell renders this impossible in the generality of 
vertebral animals, and it is not observed to happen in 
other cases where there is no such obstacle, except 
indeed it he in fishes, which are said to present a 
similar peculiarity. In such instances it cannot he 
supposed that the eggs grow, in the proper sense 
of that word; they must be considered merely 
as increasing in volume by the distention of die 
flexible envelope accommodating itself to the larva, 
which increases somewhat in size as it assimilates 
the liquid filling the interior. M. P. Huber found 
the eggs of ants when ready to he hatched nearly 
twice the size of those newly laid. Reaumur, how- 
ever, seems to be of opinion that there is a positive ab- 
sorption from without of the surrounding fluids, and 
that in the case of saw-flies and gall-flies, the veget- 
able juices are imbibed from the leaves on which they 
are fixed, in a manner which does not easily admit 
of explanation. 
As the period of hatching depends on temperature, 
it varies with, the state of the atmosphere, and the 
greater or less degree of influence with which that is 
permitted to act owing to the consistency of the egg- 
cover. The natural heat too is sometimes modified by 
the substances in which the eggs are placed, as when 
the nidus consists of dung, for example. In the heat 
of summer, the time that elapses between the depo- 
sition of the egg and exclusion of the larva is not of 
long duration ; hut it is too variable to admit of any 
general period being mentioned. In perhaps the 
majority of cases, it varies from one to ten days ; 
