486 THE INVERTEBRATA 



fall into the water. In this larva (Fig. 336), more than in any other, the 

 paired segmented tracheal gills on the abdomen show a great resem- 

 blance to paired limbs. Pupation takes place in the moist earth near the 

 water's edge. The larva of Sialis differs from those of the majority of 

 Neuroptera in that its mouth parts are of the biting type, whereas in 

 antlion larvae and the larvae of lacewings, etc., the mouth parts are 

 adapted for piercing the skin and sucking the juices of animal prey. 

 For this purpose, the points of the mandibles and maxillae are used 

 for piercing, and the mandibles, being grooved, form with the closely 

 fitting maxilla a tube up which the fluid is drawn. The carnivorous 

 habit of neuropterous larvae plays an important part in insect pest 

 control, for example, larvae of lace wing flies feed largely on aphides. 



Order MECOPTERA (Scorpion flies) 



A small order of insects distinguished by their vertically directed and 

 elongated head capsule carrying the biting mouth parts at its end; 

 two pairs of similar wings with a simple venation in which a number 

 of cross veins divide the whole area into a number of nearly equal 

 rhomboidal cells. 



The male genitalia are prominent and the terminal segments of the 

 abdomen carry them in a dorsally curved position in the manner of 

 the scorpion's tail. The cruciform larvae are caterpillar-like and may 

 possess prolegs on all segments of the abdomen. This feature, together 

 with the presence of a large number of ocelli on the head (there may 

 be twenty or more on each side), readily distinguishes these larvae 

 from those of the Lepidoptera. 



Panorpa communis, the common English scorpion fly, lays eggs in 

 crevices in the soil and the larvae hatching from these feed on decay- 

 ing organic matter. Pupation occurs in an earthen cell and the life 

 cycle is an annual one. Much information is still wanting on the life 

 histories of the members of this order. 



Order TRICHOPTERA (Caddis flies) 



Medium-sized insects with bodies and wings well clothed with hairs ; 

 mandibles vestigial or absent; maxillary and labial palps well de- 

 veloped; two pairs of membranous wings, with few cross veins and 

 held in a roof-like manner when at rest. 



The cruciform larvae are aquatic and usually live in cases formed 

 of such material as particles of wood, sand, small shells, etc. A pair 

 of hooked prolegs on the last abdominal segment which assists in 

 adhering to the case is a characteristic feature. 



The eggs are laid in or near water and the larvae quickly cover 



