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 



V 



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 



