600 TEXT-BOOK OF ENTOMOLOGY 



the Campodea-form, or campodeoid, sometimes called thysanuri- 

 form, and the cruciform. 



a. The Campodea-form type of larva 



This is the most primitive and generalized type of larva (Fig. 560). 

 A Campodeoid larva is one nearest in general shape to Campodea, 

 the form which we have seen to be the nearest allied to the probable 

 ancestor of the insects, and it also resembles the nymphs of the 

 heterometabolous insects, before the appearance of their rudimentary 

 wings. 



Brauer, in 1869, l first suggested that the larvae of a great number 

 of insects may be traced back to Campodea and lapyx. The Cam- 

 podea-form larva is active, with a more or less flattened body, well 

 developed mandibulate mouth-parts, ^and usually long legs. The 

 nearest approach to the form of Campodea is the freshly hatched 

 nymph of cockroaches (Blattidae), Forficula, Perlidae, Termitidse, 

 Psocidae, Embidee, Ephemeridae, Odonata, especially the more 

 generalized Agrionidae, the nymphs of Hemiptera, the larvae of 

 certain Neuroptera, the active pedate larvae of the more generalized 

 Coleoptera, such as those of Carabidae, Cicindelidae, Dyticidae, etc., 

 and the first larva (instar) of Stylopidse and Meloidae (Fig. ,560, d). 



While the Campodea-shape is retained throughout nymphal life, 

 of the orders above mentioned the Neuroptera and Coleoptera alone 

 have a true resting pupal stage. 



It should also be observed that great changes in the form of 

 the nymph occur within the limits of the Orthoptera; the nymph 

 of all the families except that of the Blattidae, evidently the most 

 generalized and primitive, being more or less specialized, while the 

 nymphs of the other orders all vary in degree of specialization and 

 modification. The process of adaptation once begun went on very 

 rapidly, as it has in many other orders of insects, as well as in 

 animals of other phyla. 



1 At the same date (March, 1869) we independently suggested that the insects 

 had originated from some form like the hexapodous young of Pauropus and Podura. 

 In November, 1870, we suggested that the Thysanura and the hexapodous Leptus 

 may have descended from some Peripatus-like worm. Afterwards (1871) we proposed 

 for the ancestral form the term le}itif<>nn, which was later abandoned for Brauer's 

 term Campodea-form. 



FIG. 5GO. Examples of campodeoid nymphs and larvw : a, Campodea ; b, Podura (Deprerrkn ; 

 ., I.rpisma; il, triimgrulin larva of kieloS; <. IVi-la : /, Fortieula : g, Clilot ; on: //. Mayfly (Palinge- 

 nun : /, jEschna; j, Atropos ; k, Myruieleon ; /, Sialis ; i, Corydalus ; , Cicada. 



