598 TEXT-BOOK OF ENTOMOLOGY 



slight or incomplete metamorphosis, but with a quiescent or resting 

 stage at the close of the nymph life. Lang has emphasized this 

 stage, calling attention to the fact that the fore legs of the nymph 

 of the 17-year Cicada, which lives underground on the roots of trees, 

 are thick and adapted for digging. The transition from the nymph 

 to the winged adult is signalized by the decided change in form of 

 the fore legs, as well as by the acquisition of the wings. " The last 

 larval stage is, then, what is called quiescent, i.e. the organization 

 of the imago develops within the chrysalis at the expense of the 

 accumulated reserve material." (Lang.) There seems to be a 

 resting stage, when the insect does not perhaps suck the sap from 

 the roots, and awaits in its chamber its approaching change to the 

 imago; but we should scarcely apply the term pupa to this stage, 

 though the antennae of the freshly hatched larva are larger and 

 longer than in the fully grown nymph and are distinctly 8-jointed. 



3. Hemimetabola. In this division, so named by Brauer, the 

 changes are more marked, though there is no truly inactive pupa- 

 like stage. The orders are Perlaria (Plecoptera), Odonata, and 

 Plectoptera (Ephemeridse). The freshly hatched nymphs of these 

 three groups are much alike in shape, that of Perlidae, and indeed 

 most of the Platyptera, being more generalized, unless we except 

 that of Chloeon; all closely recall Campodea, and are therefore in 

 the Campodea-stage. These nymphs are indeed more generalized 

 than the freshly hatched nymph of Blattidse, or any other of the 

 orders mentioned except the Platyptera, to which perlids belong. 

 They all have feet, and the body is more or less flattened. (Fig. 560.) 



II. Holometabola. In this division we have for the first time a 

 true larva, and a pupa stage as distinguished from the imago. More- 

 over, the insect at each stage is distinguished by radical differences 

 in form, surroundings, and in the nature of the food, while the pupa 

 is inactive, usually immovable, and incapable of taking any food, 

 and is often protected by a cocoon spun by the larva. The holomet- 

 abolous orders are the Neuroptera, Coleoptera, Mecoptera, Trich- 

 optera, Lepidoptera, Siphonaptera, Diptera, and Hymenoptera. 



As we have among worms, echinoderms, and Crustacea certain exceptional 

 species in a metamorphic group whose metamorphosis is suppressed, their de- 

 velopment being direct, so there is in pterygote insects, though in a very much 

 less degree, cases of direct development. In the wingless cockroaches such as 

 Pseudoglomeris, etc., of the tribe of Periphseriides, in some of which, however. 

 the males are winged, and in the Hemiptera, occur wingless forms such as the 

 lice and bed-bug. The Mallophaga are all wingless, while certain Dermaptc-ra 

 (Ohelidura, Anisolabis) are also apterous. The absence of wings in such cases 

 is due to disuse from parasitism, or to a life under stones or in cracks and 



