LONDON INSECTS 71 



of which there were no traces when the insect left the 

 first egg. When this is done the chrysalis skin is 

 cracked and thrown aside as useless, like the eggshell 

 of a Chicken. The difference between insects under- 

 going ' no metamorphosis ' and those undergoing ' partial 

 metamorphosis ' is merely in the stage of advancement 

 in which the egg is left. Both leave it in a more 

 developed condition than the classes of insects under- 

 going ' complete metamorphosis.' 



But as this arrangement, though a little further 

 reaching than the first, gives only three classes, and 

 these with no very clear lines between them, it is not 

 of much more value. For all practical purposes the 

 only possible classification of insects yet worked out 

 is according to the nature of their wings. 'Those 

 Hexapod insects,' writes Professor Owen still the 

 greatest authority perhaps on all such matters ' which 

 are devoid of wings are called Aptera ; those with 

 two wings only are the Diptera. All the rest have 

 four wings. The Lepidoptera have four scaly wings; 

 'the Hymenoptera have four veined wings, crossing 

 each other when at rest ; the Hemiptera have one pair 

 of wings partially thickened, and called hemelytra; 

 the Orthoptera have one pair of wings wholly thickened, 

 the other folded lengthwise; the Coleoptera have one 

 pair wholly and much thickened, called elytra, and 

 the other pair folded crosswise; the Neuroptera have 

 four reticulated wings ; the Strepsiptera have one pair 

 of wings rudimental and curled up. In the Apha- 

 niptera' which, by the bye, are not an order by 



