NOTES ON BRITISH TRICHOPTERA. 143 



naturalists, but they were unacquainted with the nature of 

 the creatures inhabiting them, and but little appears to have 

 been known of them in this respect up to the times of 

 Reaumur and De Geer. Those close observers, however, 

 give detailed descriptions of the metamorphoses of several 

 species with a minuteness that has never since been equalled. 



In this group, the case is a silken tube, to the exterior of 

 which the larva affixes various substances, varying according 

 to the species, and according to the conditions under which 

 it is placed. In the family Phryganidce, the case is a 

 straight cylindrical tube, formed of the leaves of water plants 

 and pieces of the stems or fibres cut in equal lengths and 

 arranged in a spiral manner longitudinally. One would 

 imagine that, as the larva commences its case as soon as it is 

 hatched, this would be of a taper form, and with a con- 

 siderably less diameter at one end than the other : such, 

 however, is not the case, and the diameter is nearly equal at 

 both ends ; for though the larva makes additions to one ex- 

 tremity, it at the same time is continually cutting off portions 

 at the other. This I have frequently seen them in the act of 

 doing, and it is probable that all the genera of the first group 

 have the same habit. When about to change to a pupa, it 

 fixes its case at one end to the stems of water plants, and at 

 the other draws together a few leaves or whatever substance 

 the case may be composed of, and spins within a sort of 

 grating, which admits the water but at the same time helps 

 to exclude marauding insects. 



In the family Lhnnepkilidce the forms of the cases vary 

 considerably according to the genera or species. In the 

 genus LimnephiluSy the case is always free, that is, portable, 

 and is composed of a multitude of different substances. 

 L, rhomhicusj L. Jlavicornis, and perhaps other species, 

 usually cut into short lengths vegetable fibres, which they 



