594 TEXT-BOOK OF ENTOMOLOGY 



metabola), the chief difference being the possession of the rudiments 

 of wings and the absence of a resting stage, the terms larva and 

 pupa are in reality scarcely applicable to them, and we much prefer 

 the term nymph, first proposed by Lamarck for the active " pupa " 

 of Orthoptera, Hemiptera, the Odonata and Ephemeridee, and 

 adopted in part by many. Indeed, in the more generalized and 

 older orders, the larval and pupal stages are not differentiated, 

 though the term larval, in its general sense, will probably always 

 be used; just as we speak of the larval stages of worms, echino- 

 derms, or Crustacea. 



Eaton in his elaborate work on the Ephemeridse employs the term nymph to 

 designate all the aquatic or early stages in the development of the young after 

 hatching, and he urges that the old-fashioned usage of larva and pupa seem 

 scarcely worth retention. " Nymphs are young which live an active life, quit- 

 ting the egg at a tolerably advanced stage of morphological development and 

 having the mouth-parts formed after the same main type of construction as 

 those of the adult insect." The word nymph is used in the same sense by 

 McLachlan, and by Cabot. Calvert also applies the term nymph "to the stage 

 of odonate existence between the egg and the transformation into the imago." 

 On the other hand, Brauer applies the term nymph to the pupa of holometabolous 

 insects. For larval Hyatt proposes the term nepionic. 



b. Stages or stadia of metamorphosis 



The intervals or periods between the moults or ecdyses of cater- 

 pillars and other eruciform larvae are called stages or stadia; thus, 

 as most caterpillars moult four times, we have five stages or stadia, 

 or stage (stadium) I to V. As observed by Sharp, there is, unfort- 

 unately, no term in general use to express the form of the insect at 

 the various stadia; "entomologists say, 'the form assumed at the 

 first moult,' and so on." Hence he adopts a term suggested by 

 Fischer, 1 and calls the insect as it appears after leaving the egg the 

 first instar, and what it is after the first moult the second instar, 

 and so on; hence the pupa, or chrysalis, which assumed that condi- 

 tion after moulting five times would be the sixth instar, and the 

 butterfly itself would be the seventh instar. 



c. Ametabolous and metabolous stages 



In the Synaptera development is direct, the young differing 

 neither in form, structure, or habits from the adult. Hence they 

 are said to be ametabolous. Since there is an absence of even a ten- 

 dency to a partial metamorphosis, it is evident that the insects have 

 not inherited a tendency to undergo a transformation, but that it is 

 1 Orthoptera Europaea, 1853, p. 37. 



