ENTOMOLOGY. 75 



of the shell renders this impossible in the generality of 

 vertehral animals, and it is not ohserved to happen in 

 other cases where there is no such obstacle, except 

 indeed it be in fishes, which are said to present a 

 similar peculiarity. In such instances it cannot be 

 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 the 

 lexible envelope accommodating itself to the larva, 

 which increases somewhat in size as it assimilates 

 he liquid filling the interior. M. P. Huber found 

 he eggs of ants when ready to be hatched nearly 

 wice 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. 



Ajrthe period of hatching depends on temperature, 

 t 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 ; but 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; 



