170 



AN INTRODUCTION TO ENTOMOLOGY 



The laying of eggs in compact masses, however, is not correlated, 

 in most cases, with gregarious habits of the larvae. The water- 

 scavenger beetles, Hydrophilidae, make egg-sacks out of a hardened 

 silk-like secretion (Fig. 188) ; the locusts, Acridiidse, lay their eggs in 



oval masses and cover them with a 



..- "/.v^. .-x-!.:.;^ tough substance; the scale-insects 



t?^-.': }: /:' .. .^ : :ri|y"^-.K of the genus Pulvinaria excrete a 

 :-- ;; :'.\ large cottony egg-sac (Fig. 189); 



Fig. 187 Egg-mass of the 

 squash-bug. 



F ig . 1 88. Egg-sac of Hydrophilus 

 (After Miall). 



the eggs of the praying mantis are laid in masses and overlaid with 

 a hard covering of silk (Fig. 190) ; and cockroaches produce pod-like 



egg-cases, termed 



ootheca, each 



containing many 



eggs (Fig. 191). 

 Among the 



more remarkable 



of the methods of Fi &- 1 8 9- Pulvinaria innumerabilis, females on 



grape with egg -sacs 

 caring for eggs is 



that of the lace-winged flies, Chrysopa. These insects place 

 each of their eggs on the summit of a stiff stalk of hard silk 

 (Fig. 192). 



Duration of the egg-state. In the life-cycle of most insects, 

 a few days, and only a few, intervene between the laying of 

 p. r *^ an egg and the emergence of the nymph, naiad, or larva from 

 E g g- it. In some the duration of the egg-state is even shorter, the 

 m ^ s | hatching of the egg taking place very soon after it is laid, or 

 pray- even, as sometimes in flesh-flies, before it is laid. On the 

 man? otner nan (i, in certain species, the greater part of the life of an 

 tis. individual is passed within the egg-shell. The common 

 apple-tree tent-caterpillars, Clisiocampa americana, lays 

 its' eggs in early summer; but these eggs do not hatch till the fol- 

 lowing spring; while the remainder of the life-cycle occupies only a 



