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 

 t)f 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 surface 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, CEcanthus nigri- 

 cornis; 2, CEnis semidea; 3, Piezosterum 

 siihidatum; 4, Hydrometra martini. 



Fig. 184.— Egg of the cotton- 

 worm moth; the micropyle is 

 shown in the center of the lower 

 figure. 



