56 



PHYSIOLOGY OF THE EGGS 



unfrequently concealed by elevated ridges, crossing 

 them at right angles, as under : 



Those of the Meadow Brown Butterfly (Hip- 

 parchia Jurtlna) are crowned by imbricated scales 

 like the tiles of a roof, as in the following figure : 



The period of hatching varies according to the 

 state of the atmosphere. A certain degree of heat 

 is also necessary to the exclusion of the caterpillar. 

 This heat is in most instances derived from the state 

 of the air ; but other causes sometimes produce it. 

 Those species which have several broods in the year, 

 such as the Nettle Tortoise-shell Butterfly, are 

 hatched in a few days after they are laid ; but should 

 the female lay late in the autumn, the eggs remain in 



