122 INSECT TRANSFORMATION 



have elongate narrow forewings and shorter hindwings, rela- 

 tively broad with anal folding area, the nervuration being pre- 

 dominantly longitudinal ; their wings and bodies are clothed, 

 in some cases densely, with hairs. Mandibles are wanting in 

 the winged insects which take liquid food by means of a short, 

 broad, sucking organ composed of the lobes of the labium ; 

 both maxillary and labial palps are typically developed. Their 

 larvae known as " caddis-worms " live submerged in the water 

 of ponds and streams, breathing the dissolved air by means of 

 delicate finger-like giUs carried on certain of the abdominal 

 segments, these gills are not, however, present on the newly- 

 hatched larva, but appear after the first or second moult. 

 The newly-hatched caddis grub 1 (Fig. 69 A ) is definitely campo- 

 deiform recalling in its general aspect the larva of a rove-beetle. 

 Its head carries short feelers, strong, toothed, biting mandibles, 

 and maxillae and labium in which the typical parts are, as in 

 many beetle larvae, specialized by reduction. The cuticle of 

 the thoracic segments forms firm dorsal plates and the legs are 

 relatively long and well developed ; there is a foot-segment 

 distinct from the shin, terminating in a single prominent claw. 

 The abdominal segments have distinct dorsal plates often 

 furnished with long, stiff bristles ; the tail-segment may carry 

 a pair of short appendages, sometimes jointed, bearing strong 

 hook-like claws and long flexible bristles. 



At some time after hatching, varying from a few hours to 

 several days, the young caddis begins to form a case or 

 " house " in which it finds shelter for the rest of its larval and 

 for most of its pupal life. Caddis-cases are composed of 

 material varying in different families such as plant-fragments, 

 tiny stones, shells of water-snails fastened together by a silk 

 derived from glands that open, like those of moth-caterpillars, 

 in the mouth. The important feature, in connexion with our 

 immediate subject of modification in larval form, is that, in 

 correlation with this sheltered mode of life, the cuticle of the 

 abdomen becomes relatively feebler in the older than in the 

 early caddis grub, while the thorax, thrust as a rule frequently 

 out of the sheltering " house," retains its firm protective armour 

 and its well-formed, jointed legs. Thus the advanced caddis 



1 A. J. Siltala : " Ueber die postembryonale Entwicklung der Tricho- 

 pteren-larven ". Zoolog. Jahrb., Supplement Band IX. 1907. 



