42 



larva is about to assume the pu^jal condition. Secondly, those 

 which are constantly fixed to stones or other substances. 



In the first class, the forms and conditions are very varied. 

 Speaking generally, these houses (or cases') consist of an inner 

 silken tube, to the exterior of which various extraneous substances 

 are attached. Some species {Phrygama, Neuroma, dec.) form per- 

 fectly cylindrical straight tubes of morsels of leaves and other 

 vegetable substances, beautifully arranged in a spiral manner 

 (these are not uncommon in the ponds of oiu- district), and of 

 nearly equal diameter throughout ; and the inmate is able to 

 present its head at either end indiscriminately by turning itself 

 in its case. Of course, it is apparent that the case of a young 

 larva must be much smaller and narrower than that of a full- 

 grown one. Now, with us, when we outgrow our clothes, the 

 tailor is usually applied to for a fresh suit, and the old ones are 

 discarded : but with Caddis-worms it is ordinarily dififerent ; the 

 creature does not come out of its case and thus expose itself to 

 danger while manufacturing a new house, but it ingeniously cuts 

 off from time to time the end portion that has become too small, 

 and goes on adding simultaneously to the other end. This will 

 apply to all the tubular cases. A very common form (Anaholia) still 

 occurring abundantly in our little river Ravensbourne, is a tube of 

 fragments of gravel and sand, and as the larva lives in running 

 water, and might be in danger of being swept away by the current, 

 there are attached to this tube long ft-agments of small twigs 

 which serve probably as balancers. Some of the most interesting 

 forms are those in which the exterior of the case is ornamented 

 with shells (often containing their living inmates), seeds of water- 

 plants, fragments of water-beetles, and even the cases of the 

 smaller species of the same group. These are mostly constructed 

 by species of Limnophilus, and the same species will often use a 

 variety of materials according to the conditions in which the larvae 

 are placed. Sometimes comparatively large shells are used, some- 

 times myriads of minute shells to the number of several 

 hundreds, beautifully arranged in mosaic, are wholly employed, 

 sometimes wholly the seeds of some particular water plant, some- 

 times portions of the case wholly of one material and the other 

 portion of another, and finally, all these substances, combined 

 with sand, gravel, and vegetable matters, are sometimes arranged 

 indiscriminately oh one and the same case. These shell cases are 



