CONSTRUCTION OF EGGS. 



25 



up in a ring, as is distinctly shown in many of the 

 beautiful and accurate figures of Sepp *. 



a, egg of the privet hawk-moth (^Sphin.v lAgustri) magnified, 

 showing Jhe inclosed embryo, b, the caterpillar when grown. 



In the case of the eggs of birds, the chick, when 

 fully developed, breaks the shell with its bill, the 

 point of which is then furnished with a hard scale. 

 This is evidently contrived by providential wisdom for 

 this very purpose, for it drops off in a few days after 

 the chick is excluded. It is probable that the larvae of 

 many insects which are furnished with strong man- 

 dibles gnaw their way through the egg-shell ; but we 

 know that there are others which, like the spider, 

 rupture their envelope, since the edges appear ragged 

 and irregular. Others, again, seem to have an open- 

 ing provided for them, in a door, which only requires 

 them to push it open. This is the case with the louse 

 {Pediculus humanus), and with the bird-louse 

 {Nirmus), found on the neck feathers of the golden 

 pheasant. A still more ingenious contrivance was 

 discovered by the Rev. R. Sheppard, in the egg of a 

 field-bug {Pentatoma, Latr.), which is not onlyfur- 

 * Der Woiidercn Gods, passim. 



