vi] LARVAE AND THEIR ADAPTATIONS 63 



more primitive Lepidoptera. The caddis-larva is as 

 a rule of the cruciform type, but with well-developed 

 thoracic legs, and with hook-like tail-appendages ; by 

 means of the latter it anchors itself to the extremity 

 of its curious 'house.' It is of interest to note that 

 in the earlier stages of some caddises lately described 

 and figured by A. J. Siltala (1907), the legs are rela- 

 tively very long, and the larva is quite campodeiform 

 in aspect. Some of these caddis-grubs retain the 

 campodeiform condition and do not shelter perma- 

 nently in cases, as their relations do. Different genera 

 of caddises differ in their mode of building. Some 

 fasten together fragments of water- weeds and plant 

 refuse, others take tiny particles of stone, of which 

 they make firmly compacted walls, others again lay 

 hold of water-snail shells, which may even contain 

 live inhabitants, and bind these into a limy rampart 

 behind which their bodies are in safe hiding. 



The silk with which the 'caddis-worms' fasten 

 together the materials for their houses is produced 

 from spinning-glands which like those of the Lepido- 

 ptera open into the mouth. 



The survey of the various types of beetle-larvae 

 enumerated above (pp. 50-56) concluded with a short 

 description of the legless grub, which is the young 

 form of a weevil or a bark-beetle. This is a larva 

 in which the head alone has its cuticle firm and hard ; 

 the rest of the body is covered with a pale, flexible 



