i8 ANATOMY AND MORPHOLOGY OF INSECTS. 



is attended by periodic sheddings of the cuticular layers of the 

 skin, which are known as ecdyses, or moults. 



Before each ecdysis the hypodermis separates from the 

 cuticle, and a new cuticle is formed beneath the old one. The 

 new cuticle remains soft and extensile for some time after the 

 old cuticle is shed, and so permits of a considerable increase of 

 size. This is effected generally in insects by the expansion of 

 the air-vessels. The new cuticle then becomes hard and inex- 

 tensile, checking all further increase in size until the next ecdysis. 

 Not only the external cuticle, but the cuticular lining of the 

 alimentary canal and of the tracheae, is shed at each ecdysis. 



Metamorphosis. These periodic ecdyses are sometimes at- 

 tended by great and apparently sudden changes of external 

 form, habits, and structure, known as metamorphoses ; thus 

 three stages are commonly recognised in the life-history of an 

 insect : the larva, the pupa or nymph, and the imago or perfect 

 form. 



The Larva. Amongst the spring-tails (Thysanura), the curious 

 genera Campodea and Sapyx closely resemble the newly-hatched 

 larvae of many insects of widely different orders ; such hexapod 

 larvae are spoken of as exhibiting the campodea form. The May- 

 fly (Cloeon diptera) is developed from such a larva by a series of 

 many moults, without any marked change of form before the 

 last moult. The Earwig (Forficula) is developed in the same 

 manner, but more rapidly with fewer moults ; and the Rove- 

 beetles (Staphylinidce) have a campodea larva, but pass through 

 a nymph stage before they attain sexual maturity. 



Certain Coleoptera, Sitaris, Meloe and its allies, the genus 

 Mantispa amongst the Orthoptera, and probably many other 

 insects (Brauer*), are hatched as active campodea larvae, but 

 soon lose their legs and become grubs, probably at the first 

 moult. This phenomenon was called hypermetamorphosis by 

 Faivre. The grubs are parasites on other insects, and after 

 attaining their full size become nymphs. 



* Brauer, F., ' Beschreibung der Verwandlungsgeschichte der Mantispa 

 Styriaca und liber die sogannte Hypermetamorphose Faivre's.' Verb. Zool.- 

 Bot. Gesellsch., Wien, Bd. xix., 1869. 



