According to Kirby and Spence there is a kind of caterpillar (_Pieris cratægi_) which lives in little colonies of ten or twelve in common chambers lined with silk. In one part they make of the same material a little bag or pocket, which is used by the community or household as a water-closet. When full of excrement the caterpillars empty it by turning out the pellets with their feet.[109] Only two other instances of noteworthy intelligence as exhibited by larvæ have fallen within my reading. One of these is mentioned by Réaumur, who says that the larvæ of _Hemerobius chrysops_ chase aphides, and having killed them, clothe themselves in their skins; and the other case is the very remarkable one mentioned in his newly published work by W. MacLachlan, F.R.S., of caddis-worms adjusting the specific gravity of their tubes to suit that of the water in which they live, by attaching heavy or light material to them according as they require sinking or flotation. FOOTNOTES: [90] Quoted by Bingley, _Animal Biography_, vol. iii., p. 118. [91] _Loc. cit._, p. 344. [92] Büchner, _loc. cit._, p. 344. [93] Quoted in Strauss, _Insects_, s. 389. [94] Kirby and Spence, _loc. cit._, pp. 321-2. [95] _Life and Recollections_, vol. ii., p. 356. [96] Quoted by Bingley, _loc. cit._, vol. iii., pp. 150-51. [97] _Gleanings_, vol. ii., pp. 165-6. [98] _American Journ. Sc. and Art_, vol. x., Oct. 1875. [99] _Animal Biography_, vol. iii., pp. 244-5. [100] _Nature_, vii., p. 49. [101] _Intr. to Ent._, ii., p. 475. [102] _Ibid._, p. 475. [103] _[OE]uvres_, ix., p. 370. [104] _Trans. Ent. Soc._, vol. ii. [105] _Introd. Ent._, Letter xi. [106] Westwood, _Trans. Ent. Soc._, vol. ii., p. 1. [107] Kirby and Spence, _Entomology_, Letter xvi. [108] _Trans. Ent. Soc. France_, vol. i., p. 201. [109] _Introduction to Entomology_, Letter xxvi. CHAPTER VIII. FISH.