XII] ORDERS OF INSECTS 251 



Order I. Aptera. 



Wingless Insects, with scales and hairs covering the body. 

 The mouth-parts are adapted for biting. They move by running or 

 by springing by aid of a caudal style which is kept bent forwards 

 under the abdomen and retained in this position by a ventral hook. 

 When released from this hook the recoil of this style hurls the 

 insect into the air. The segments of the thorax are not fused 

 together and there is no metamorphosis. 



Not all wingless Insects belong to this order. The name 

 Aptera (Gr. aTrrepos, wingless) refers to the belief that the ancestors 

 of these Insects never had wings and that thus they represent a 

 lower stage of evolution than the rest of the sub-class. 



For the most part the Aptera are minute Insects living in 

 retired spots under leaves or rubbish, in roof-gutters, etc., but they 

 are widely distributed over the world. One of the best known is the 

 Silver-fish, Lepisma, which hides in disused cupboards, old chests of 

 drawers, sugar barrels, etc. It runs with great rapidity. Machilis is 

 a small insect found between tide marks in seaweed. In it the 

 abdominal exponents have small vestigial appendages. 

 Order II. Orthoptera. 



The Orthoptera (Gr. op0os, straight; irrepoV, a wing) have mouth- 

 parts adapted for biting. The anterior wings are as a rule stiff, 

 and when the Insect is at rest one overlaps the other, and both 

 usually cover and conceal the large membranous hinder wings with 

 which the creature flies. There is an incomplete metamorphosis, 

 the young being at first without wings. 



This order is a very varied one and doubts exist as to whether 

 it is a natural one. It includes the Cockroach, whose anatomy has 

 already been described ; the Earwig, Forficula ; the praying insect, 

 Mantis; the leaf and stick insects, Phyllium and Phasma; the 

 Grasshopper (Fig. 100), Pachytylus', the Locust, Locusta; the 

 Cricket, Gryttus ; and many others. 



Order III. Paraneuroptera, or Dragon-flies. 



The Paraneuroptera (Gr. vevpov, a tendon and hence a nervure) 

 have biting mouth-parts. Both pairs of wings are membranous and 

 used in flight, and the " veins " of the wings form a more or less 

 close network. Metamorphosis is incomplete. 



