66 INTRODUCTION. 



attaching them to the plant and defending them from 

 the action of the weather. They differ essentially from 

 the eggs of birds, as no hme entei-s into their composi- 

 tion, and, instead of being covered with a crustaceous 

 shell, they are merely enveloped by a thin membrane. 

 They are also very unlike each other in different 

 species, whether we regard them in respect to co- 

 lour, form, or sculpture. Some of them are nearly 

 orbicular or oval, others cylindrical, and not a few 

 conical The surface is often beautifully carved, as 

 will be seen by the accompanying figures, which re- 

 present several varieties, as they appear when highly 

 magnified. Plate I. fig. 3, Egg of Vanessa urticcB, 

 with several longitudinal ridges. Fig. 4, Subcorneal 

 egg of Pontia brassic(B, with granulated longitudinal 

 ribs, connected by elevated cross lines ; the colour 

 bright yellow. Fig. 5, Egg of Hippnrchia Tithomis. 

 Fig. 6, Of Hipparchia Jiirtina, crowned with a se- 

 ries of imbricated scales. Fig. 7, Globular egg of 

 Hipp. HyperanthuSf ornamented with regular rows 

 of minute elevated points. Fig. 8, Egg of Hipp. 

 CBgeria, having the whole surface covered with hex- 

 agonal meshes. 



After the fly has fixed her eggs on a plant, she 

 takes no further care of them, but leaves them to be 

 hatched by the heat of the atmosphere. This gene- 

 rally takes place in the course of a few days, but the 

 period varies according to the degree of warmth to 

 which they are subjected, and the greater or less 

 density of the shell or outer covering. Such, indeed, 



