254 



• KNOWLEDGE ♦ 



[Sept. 20, 1884. 



of sand or small stones, the leaves of trees or frsgoQeuts ot 

 aquatic vegetation, the seeds of rushes or other plants 

 growing by the water side, and the shells of fresh-water 

 mollusca, both dead and living — these are some of the 

 principal materials employed, their exact nature and 

 iirrangement being difl'ereiit in diflerent species, and some- 

 times in the same species at different ages. Some will cut 

 Httle shreds of vegetable matter, all of the same length, and 

 arrange them side by side in a spiral manner with won- 

 derful regularity ; others will take -whole leaves of poplar, 

 willow, and other trees, and attach them flatly to the case. 

 Some will select small stones, and stick them on with great 

 dexterity, forming a tube which reminds one forcibly of the 

 exquisite structure made by the marine worm Arenaria 

 bel</ica, which occurs not unfrequently on our sandy sea- 

 shores. Others will strengthen their tube with very fine 

 grains of sand, making a case in shape like an elephant's 

 tusk. Some will select straight bits of stick or 

 rush, and place them longitudinal!}', when they will 

 sometimes project far beyond the ends of the caselike 

 handles ; ethers, using the same materials, but in shcuter 

 pieces, will place them transversely, putting each piece 

 tangeotially to the surface, Eo that the ends furm a perfect 

 •r/icvaux da frise rciund the case, which, if looked at down its 

 length, reminds one of a stocking carrying set after set of 

 the needles with which it has been knitt^d. But unques- 

 tinnably the most interesting are those that are adorned 

 with shells. Caddis-worms are excellent conchologists, and 

 by obtaining a number of their cases you may get together 

 .t very respectable collecti( n ot freshwater shells. Some- 

 times you get the same shell throughout, when the case is 

 often extremely elegant and symmetrical; but frequently 

 you may find five or six species on one case, and then, if 

 the shells are very dissimilar, of course the symmetry of the 

 structure is destroyed. The most elegant are those fnrnied 

 of the smaller species of I'hinorlis, flit, spirally coiled 

 shells, something like tiny snakes rolled up. Of these 

 elegant little oV)jects sometimes as many as fifty speci- 

 mens go to adoin a single caddis case. Then there 

 are the smaller kinds of Zimnma, conical, spirally- 

 twisted shells of delicate texture, one or two of which 

 may fometimes be fcjund filling up odd corners, while, 

 projectiog here and there, like so many excrescences, 

 may perhaps be seen the stouter and broader shells of 

 flythinus, the mouth of which is closed by a sort of trap- 

 door. Again, we may find the much smaller and more 

 depressed spiral s-hells of Vahata, which, with the spires 

 ,(.11 turned inwards, sometimes compose almost the whole 

 case, and, lastly, stuck in here and there wherever there is 

 room, the simply conical abodes of the tiny freph-water 

 limpets belonging to the genus Ancijlus. But, besides all 

 these, there are the shells made up of two similar parts 

 hinged togeiher — bivalves, as they are called — belonging 

 to the genera Sphcnrntm and Pisidium ; sometimes a single 

 \-alve is used, but more frequently the pair, especially of 

 the very common species called SpJuKrium corneum. This 

 is a tolerably bulky s-hell, and often exceeds in diame'er 

 the case which it adorns, so that if three or four ot them 

 are used on one case, it acquires a very irregular form. It 

 is not always dead shells that are chosen ; very frequently 

 living molluscs are made use of just as they are, though 

 their consent to the arrangement does not appear to be 

 sought, and the plans of their life must be greatly inter- 

 fered with by this unceremonious attachment. Mr. 

 McLachlan, the historian of the European Trichoptera, 

 ^Ays that he has seen the wing-cases of water beetles some- 

 times mixed with other things as ornaments to the cases, 

 and even the cases of other and smaller caddis-worms, and 

 tiuit, too, while they still contained their inhabitants. The 



means of attachment of all these objects is the same silky 

 secretion that lines the tube. 



The operations of the insect in the construction of its 

 domicile are very interesting, and may be watched by any 

 one who will take the trouble to eject one from its dwellicg 

 and provide it with materials for the formation of another. 

 The two following instances are from the records of the 

 continental observers, Mejer and Pictet. The first refers 

 to the formation of a vegetable case. A larva, deprived of 

 its case, seized a piece of reed, and bit ofi" from it a portion 

 of the requisite length ; then, cutting a slit in one side, it 

 crawled in and closed up the rent with silk and vegetable 

 debris, and there was the case, fully made. When pieces 

 of reed too short for the case were intentionally given to 

 it, it pieced them out to the required length by cutting oS^ 

 fragments of leaves and attaching them to one end. The 

 other refers to the formation of a mineral case. The larva 

 collected two or three smooth stones of moderate size, and 

 made a low arch by fastening them together with silken 

 threads ; then placing itself under this arch, it took up one 

 stone after another, and, with its feet, fitted them in as 

 carefully as a bricklayer would lay his bricks, attaching 

 them to the neighbouring stones when satisfied as to their 

 position. The stones were always placed smooth side in- 

 wards. In this way it took between five and six hours to 

 complete the case. 



If the case should be made too long, pieces are cut off 

 till the right length is obtained. As not only the length, 

 but also the width of the case, is always suited to the size 

 of the animal, it becomes interesting to inquire how the 

 provision is made for growth in diameter ; as the creature 

 grows, each new circle added at the anterior extremity is 

 made of rather larger diameter, thus giving the whole tube 

 a somewhat conical shape ; then the smaller end is cut off, 

 and so by repeated additions to one end and subtractions 

 from the other, the ease is always the right size, and thus 

 one can understand how it is that a caddis which begins 

 life with a leafy case may, perhaps, end it with a stony or 

 shelly one, and that too without ever quitting its tenement. 

 Some species do not seem to be at all particular as to the 

 materials they use, but others are so fastidious that they 

 will rather go unclothed (which, of course, means epeedy 

 death) than adopt the wrong material. 



The cases hitherto referred to are free, and the larva drags 

 its abode about with it as it crawls slowly along with just 

 so much of its body projecting from the case as carries the . 

 three pairs of legs. But many, especial ly of the smaller species, 

 and those that live in very rapidly-running water, make 

 cases which are attracted to stones, and consist of oval, 

 irregular masses of fragments of stones. Some, again, live 

 in companv under a common covering of vegetable debris 

 fastened together with silken threads, while others form on 

 the surface of large stones silken canals covered with slime 

 and mud. These latter are supposed to be, to a great 

 extent, carnivorous, feeding on other aquatic larvw ; but 

 the larger kinds are, as a rule, vegetable feeders, eating the 

 leaves of various water plants, which, when adult, they 

 devour entirely, beginning at the edge, but when young 

 they satisfy themselves with the tender green parts between 

 the veins of the leaf, which are more suited to their 

 juvenile capacities than the tougher veins themselves. 

 They will, however, take to animal food when necessary, 

 and will even, ou occasion, turn cannibals, 

 {To be continued.) 



JIr. Bmn, the chess-player, has iu the press a tract in which he 

 jirupoiinds and analyzes an early variation ot the commonest 

 opening, which has for some vpars been associated with his name. 

 The publisher will be Mr. Wade, ot Tavistock-street.— JMenirum. 



