XXI 



INSECTA: NEUROPTERA 



317 



opaque the characteristic which has led to these forms being 

 sometimes grouped in a special order, the Trichoptera. The 

 nervature of the wings is peculiar in having very few trans- 

 verse nervures (Fig. 240). The 

 broad hind wings are folded fan- 

 wise under the front wings when 

 at rest, the latter being merely 

 laid obliquely over the back and 

 sides, as in the alder-flies. There 

 is a well-marked metamorphosis 

 with a quiescent pupal stage, which 

 takes place below the water. The 

 pupa, however, just before moult- 

 ing the pupal skin, becomes active, and swims to the surface. 

 The antennae of the imago are thread-like, and the mouth- 

 parts are reduced, the mandibles being absent or very 

 rudimentary, though present in the pupa (see p. 324). 



V 



FIG. 240. Caddis-fly. 



Eggs. 



Life-history of a Caddis-fly. 



The rather moth-like, dull-coloured Caddis-flies are often 

 to be seen on plants by the water side, or flying rather feebly 

 close by (Plate III., /). 



The eggs are laid in the summer, in a mass 

 surrounded by jelly. They are either dropped by 

 the female at the water surface, or in some cases she is said 

 actually to enter the water and deposit the mucilaginous egg- 

 mass on some water-plant stem, or other object (Plate III., E). 

 The egg-mass is sometimes in the form of a jelly-like rope, 

 which may be an inch or more long, or it may be a ring, 

 or simply a flat disc of jelly. The eggs, which are often 

 greenish in colour, are clearly to be seen inside. 

 The Larvae The larvae hatch out after two to three weeks, 

 or Caddis- and at once begin to make for themselves little 

 worms, protective cases out of any suitable material that 

 may be at hand in the water. When the larva is full grown, 

 its case has usually a characteristic appearance according 

 to the species which has made it. One such case is shown in 

 Fig. 242, P, with the caddis-worm projecting from one end. 

 The larva under normal conditions never exposes more than 

 its head and the first three segments of the body, all of 



