METAMORPHOSIS 157 



alterations of form. On the other hand, the butterfly under- 

 goes but little modification, remaining much in the condition 

 shown by A, Fig. 85, till the fourth, or penultimate, ecdysis, 

 but then suffers a complete change of form and condition, which 

 apparently is only inferior to another astonishing change that 

 takes place at the fifth or final moult. The chief, though by no 

 means the only, difference between the two series consists in the 

 fact that the butterfly has interposed between the penultimate 

 and the final ecdyses a completely quiescent helpless condition, in 

 w r hich it is deprived of external organs of sense, locomotion, and 

 nutrition ; while in the locust there is no loss of these organs, and 

 such quiescent period as exists is confined to a short period just 

 at the fifth ecdysis. The changes exhibited by the butterfly are 

 called " complete metamorphosis," while this phenomenon in the 

 locust is said to be " incomplete." The Insect with complete 

 metamorphosis is in its early stage called a larva, and in the 

 quiescent state a pupa. The adult state in both butterfly and 

 locust is known as imago or perfect Insect. 



The most conspicuous of the differences between Insects with 

 complete and those with incomplete metamorphosis is, as we 

 have remarked, the existence in the former of a pupa. The 

 pupal state is by no means similar in all the Insects that 

 possess it. The most anomalous conditions in regard to 

 it occur in the Order Neuroptera. In some members of 

 that Order the Caddis-flies for instance the pupa is at first 

 quiescent, but becomes active before the last ecdysis ; while in 

 another division the May-flies the last ecdysis is not preceded 

 by a formed pupa, nor is there even a distinct pupal period, but 

 the penultimate ecdysis is accompanied by a change of form to 

 the winged condition, the final ecdysis being merely a casting of 

 the skin after the winged state has been assumed. In the 

 Odonata or Dragon-flies there is no pupal stage, but the change 

 of form occurring at the last ecdysis is very great. In those 

 Insects where the interval between the last two moults is not 

 accompanied by the creature's passing into a definite, quiescent 

 pupa, the individual is frequently called then a nymph ; but the 

 term nymph has merely a distinctive meaning, and is not capable 

 of accurate definition, owing to the variety of different conditions 

 covered by the word. Eaton, in describing this term as it is used 

 for Epliemeridae, says, " Nymphs are young -which lead an 



