THE METAMORPHOSIS OF INSECTS 



167 



the more common type of insect eggs, those that are laid while still 



enclosed in their shell. 



The shape of the egg. The terms ovoid and ovate have a definite 



meaning which has been derived from the shape of the eggs of birds ; 



but while many eggs of 

 insects are ovate in form, 

 many others are not. 



The more common 

 form of insect eggs is 

 an elongate oval, some- 

 what curved; this type is 

 illustrated by the eggs 

 of crickets (Fig. 183, i); 

 many eggs; are approx- 

 imately spherical, as those 

 of some butterflies (Fig. 

 183, 2) ; while some are of 

 remarkable shape, two of 

 these are represented in 

 Figure 183,3, 4. 



The sculpture of the 

 shell. Almost always the 

 external ^surf ace of the shell 



of an insect egg is marked with small, hexagonal areas ; these are the 



imprints of the cells of the follicular epi- 

 thelium, which formed the shell. In 



many cases the ornamentation of the 



shell is very conspicuous, consisting of 



prominent ridges or series of tubercles ; 



this is well -shown in the eggs of many 



Lepidoptera (Fig. 184). 



The micropyle. It has been shown, 



in the course of the discussion of the 



reproductive organs of the female, that 



the egg becomes full-grown, and the 



protecting chorion or egg-shell is formed 



about it before it is fertilized. This 



renders necessary some provision for the 



entrance of the male germ -cell into the 



egg; this provision consists of one or 



more openings in the shell through which a spermatozoan may enter 



This opening or group of openings is termed the micropyle. 



Fig. 183. -Eggs of insects; I, (Ecanthus nigri- 

 cornis; 2, (Enis semidea; 3, Piezosterum 

 subulatum; 4, Hydrometra martini. 



Fig. 184. Egg of the cotton- 

 worm moth; the micropyle is 

 shown in the center of the lower 

 figure. 



