INSECTS 377 



cases a refuge chamber branches out of the nest, from which it 

 is separated by another neatly-made door, and it may also have a 

 direct communication with the exterior of similar kind. 



LIFE-HISTORIES, &c, OF INSECTS (Insecta) 



Many well-known insects, e.g. Bees, Butterflies, and Beetles, 

 are striking illustrations of indirect development. They hatch 

 out from the eggs as larvce, which are exceedingly unlike the 

 adult form, and pass later on into a quiescent pupa stage, from 

 which the perfect insect or imago finally emerges. In such cases 

 we may speak of a complete metamorphosis. There are also 

 numerous instances where, as in Earwigs and Cockroaches, the 

 just-hatched young differ far less from their parents, the char- 

 acter of which they gradually assume without, as a rule, passing 

 through a quiescent stage. It is then convenient to speak of 

 nymphs, not of larvae, and the metamorphosis is said to be 

 partial. And there are also some insects which begin life in a 

 form which differs so little from the adult that the use of the 

 term metamorphosis is hardly justifiable. 



The time which elapses before an insect's ^<g'g hatches out 

 varies greatly in different cases, and so does that consumed in 

 the life-history taken as a whole. Hatching may take place on 

 the day of laying, as in some Flies, or eggs deposited in late 

 summer may remain dormant until the following spring, as 

 in some Moths. The most remarkable case of a protracted 

 life-history is afforded by the Seventeen-year Cicada {^Cicada 

 septendecim), which exists as a larva for the period indicated by 

 its name (see vol. ii, p. 217). 



A.— INSECTS WITH PARTIAL METAMORPHOSIS 



Primitive Wingless Insects (Aptera). — Little is known as 

 to the life-history of the Tassel-tails and Spring-tails which con- 

 stitute this order, but many of them, though not all, closely 

 resemble the adult stage at the time of hatching. More obser- 

 vations are badly needed, and might easily be made, for these 

 little creatures are abundant almost everywhere. 



Straight- Winged Insects (Orthoptera). — The appearance 

 of the different stages in the life-history of the Common Earwig 



Vol. III. 87 



