TRICHOPTERA 



557 



Fig. 686. — Two egg-masses 

 of caddice-fliesra, Phryganea 

 interrupta; b, Tricenodes sp. 

 (From Lloyd.) 



distance before the apex ; these are larger than the spine-like sets 



and are usually differently colored. The ntimber of these spurs is 



much used in classification. 



The eggs of caddice-fiies are round or slightly oval in form. 



They are laid either in water or upon objects above water from which 



the larvcB when hatched can find their 



way into the water. Some species that 



lay their eggs in water descend below the 



surface in order to glue their eggs to some 



submerged support. So far as is known, 



all species of cadd ice-flies, except some 



of the Rhyacophilidas, lay their eggs in 



a mass enveloped either in a cement, by 



which the mass is glued to some support, 



or in a gelatinous covering. In the latter 



case, the covering absorbs water and thus 



increases greatly in size. The form of the 



gelatinous mass and the arrangement of the eggs within it are often 



characteristic of the species (Fig. 686). 



The larvse of most caddice-flies, the caddice-worms, are somewhat 

 caterpillar-like (cruciform) in shape (Fig. 

 687) ; but some are more nearly campodei- 

 form. Those that are eruciform build a 

 portable case in which they live; most of 

 the campodeiform larvas do not build port- 

 able cases. In the eruciform larvae the 

 head is bent down, as in a caterpillar; in 

 the campodeiform larvse the head is hori- 

 zontal, the mouth-parts projecting for- 

 ward. Both types differ from the cater- 

 pillars in having only one pair of prolegs, 

 the anal prolegs. These are each furnished 

 with a chitinous hook. The mouth-parts 

 are fitted for chewing. The thoracic legs 

 are well developed. In the case-building 

 forms, the first abdominal segment often 

 bears three tubercles, one dorsal and one 

 on each side; these are the "spacing- 

 himips," and serve to keep a space between 

 the insect and its case for the free circu- 

 lation of water for respiration. In several 

 families the larvce possess abdominal tra- 

 cheal gills; these are filamentous and are 

 sometimes branched; they arise singly 

 or in tufts. With the exception of a single 

 European genus, Enoicyla, all caddice- 

 worms are aquatic. 

 Most caddice-worms build portable cases in which they live and 



which they drag about wherever they go, projecting only the front 



Fig. 687. — ^A caddice-worm, 

 Anabolia nervosa: A, larva 

 extracted from its case; 

 B, one of the dorsal spaces 

 of the abdominal seg- 

 ments more strongly mag- 

 nified. (From Sharp.) 



