

DEVELOPMENT 14! 



mm. in width; the oval eggs of the cecropia moth, 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 particular 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. 211. 



Always the chorion is penetrated by one or more openings, constitut- 

 ing the micro pyle, for the entrance of spermatozoa. 



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 to fasten the eggs to appropriate 

 objects, such as food plants, the skin of other insects, the hairs of 

 mammals, etc.; it may form a pedicel, or stalk, for the egg, as in 

 Chrysopc, (Fig. 212); may surround the eggs as a gelatinous envelope, 

 as in caddis flies, dragon flies, etc.; or may form a capsule enclosing the 

 eggs, as in the cockroach. 



The number of eggs laid by one female differs greatly in different 

 species and varies considerably in different individuals of the same 

 species. Some of the fossorial wasps and bees lay only a dozen or so and 

 some grasshoppers two or three dozen, while a queen honey bee may lay 

 a million. Two females of the beetle Prionus laticollis had, respectively, 

 332 and 597 eggs in the abdomen (Mann). A. A. Girault gives the fol- 

 lowing numbers of eggs per female, from an examination of twenty egg- 

 masses of each species: 



MAXIMUM MINIMUM AVERAGE 



Thyridopteryx ephemera formis (bagworm). . . . . 1649 465 941 



Malacosoma americana (tent caterpillar) 466 313 375-5 



Chionaspis fur jura, (scurfy scale) 84 33 66 . 5 



Hatching. Many larvae, caterpillars for example, simply eat their 

 way out of the egg-shell. Some maggots rupture the shell by contor- 

 tions of the body. Some larvae have special organs for opening the 

 shell; thus the grub of the Colorado potato beetle has three pairs of 

 hatching spines on its body (Wheeler) and the larval flea has on its head 

 a temporary knife-like egg-opener (Packard) . The process of hatching 

 varies greatly according to the species, but has received very little 

 attention. 



