NYMPHS AND PTJP^ 63 



correlated modifications. This instar, in its turn, may be followed 

 by an apodous stage which is well exhibited in the Meloidae. In 

 the Strepsiptera the campodeiform first larvae instar is directly 

 followed by an apodous stage. 



In a few words, it may be said that Berlese's theory co-ordinates 

 and explains the significance of diverse larval types which can 

 only, otherwise, be interpreted as intercalated and purely adaptive 

 phases. 



Nymphs and Pupae. The general characters of the nymphs of 

 the Hemimetabola have already been referred to. Nymphs 

 share many features in common with campodeiform larvae, but, 

 on the other hand, they exhibit in their visual organs and in the 

 developing external rudiments of wings and genitalia features 

 which appear only in the pupal instar among Holometabola. In 

 other words, nymphs have attained a more advanced stage of 

 ontogenetic development than larvae, and the protopod, polypod 

 and the true oligopod phases are passed through in the egg. In 

 the Hemimetabola the nymphal instars are preparatory to the 

 development of the imago, while in the Holometabola the larval 

 instars are preparatory to the development of the pupa. We may, 

 therefore, conclude that the pupa, along with the antecedent 

 prepupa, are the ontogenetic counterparts of the nymphal instars 

 of the lower orders of insects. It seems that tachy genesis, or 

 shortening of development, has resulted to the extent that the 

 whole series of nymphal instars has become concentrated into 

 these two stages, with the elimination of intervening ecdyses. 

 In support of this contention we may pause to consider certain 

 groups of Hemimetabola, which already exhibit well-defined 

 tendencies towards the holometabolous condition. Thus, among 

 the Coccidae definite evidence of a pupal instar occurs in the males. 

 Furthermore, in this family the insect leaves the egg not as a 

 nymph, but as an oligopod larva. In the sub-family Diaspinae 

 an apodous instar follows, and this, in its turn, is succeeded by 

 three quiescent nymphal instars delimited by separate ecdyses. 

 These nymphal instars are unquestionably incipient pupal stages, 

 and much the same condition prevails in Thysanoptera, except 

 that there are but two such stages. Among the Holometabola 



