i6o 



ENTOMOLOGY 



quite fantastic, 

 in Fig. 207. 



FIG. 208. 



Something of the variety of form is shown 

 As regards size, most insect eggs can be 

 distinguished by the 

 naked eye; many of 

 them tax the vision, 

 however, for example, 

 the elliptical eggs of 

 Cecidomyia legumini- 

 cola, which are but 

 .300 mm. in length 

 and .075 mm. in 

 width; the oval eggs 

 of the cecropia moth, 



Three eggs of the cabbage butterfly, Pieris 

 rapce. Greatly magnified, but all drawn to same 

 scale. 



FIG. 209. 



on the other hand, are as long as 3 mm. 



The egg-shell, or chorion, secreted 

 around the ovum by cells of the ovarian 

 follicle, may be smooth but is usually 

 sculptured, frequently with ridges 

 which, as in lepidopterous eggs, may 

 serve to strengthen the shell. The 

 ornamentation of the egg-shell is often 

 exquisitely beautiful, though the par- 

 ticular patterns displayed are probably 

 of no use, being incidentally produced 

 as impressions from the cells which 

 secrete the chorion. Variations of 

 form, size and pattern are frequent in 

 eggs of the same species, as appears in 

 Fig. 208. 



Always the chorion is penetrated by 

 one or more openings, constituting the 

 micro pyle, for the entrance of sperma- 

 tozoa. 



As a rule, the eggs when laid are accompanied by a fluid of 

 some sort, which is secreted usually by a cement gland or 

 glands, opening into the vagina. This fluid commonly serves 



Chrysopa, laying eggs. 

 Slightly enlarged. 



