I 5 8 METAMORPHOSIS 



active life, quitting 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 intervals between the ecdyses are called stadia, the first 

 stadium being the period between hatching and the first ecdysis. 

 Unfortunately no term is 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. To avoid this circum- 

 locution it may be well to adopt a term suggested by Fischer,^ 

 and call the Insect as it appears at hatching the first instar, 

 what it is as it emerges from the first ecdysis the second instar, 

 and so on ; in that case the pupa of a Lepidopteron that assumed 

 that condition at the fifth ecdysis would be the sixth instar, and 

 the butterfly itself would be the seventh instar. 



Various terms are used to express the differences that exist in 

 the metamorphoses of Insects, and as these terms refer chiefly to 

 the changes in the outer form, we will here mention them. As 

 already stated, the locust is, in our own language, said to have an 

 incomplete metamorphosis, the butterfly a complete one. The 

 term Holometabola has been proposed for Insects with complete 

 metamorphosis, while the appellations Ametabola, Hemimetabola, 

 Heterometabola, and Paurometabola have been invented for 

 the various forms of incomplete, or rather less complex, meta- 

 morphosis. Some writers use the term Ametabola for Insects 

 that are supposed to exhibit no change of external form after 

 quitting the egg, the contrasted series of all other Insects being 

 then called Metabola. Westwood and others use the word 

 Homomorpha for Insects in which the condition on hatching 

 more or less resembles that attained at the close of the develop- 

 ment, and Heteromorpha for those in which the form on 

 emergence from the egg differs much from what it ultimately 

 becomes. 



Hypermetamorphosis. 



There are certain unusual chano-es to which the term 

 hypermetamorphosis has been applied ; these we can here only 

 briefly allude to. 



^ Trails. Linn. Soc, 2nd Series, "Zool." 1888, iii. p. 12. 

 ^ Orthoptera euTo;paea, 1853, p. 37. 



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