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Show 246 DISIN'l'EGHA'l'ION CnAP. V. therefore nece~sary to obtain flints for building purposes from the bed of red clay over] ying the chalk (the residue of its dissolution by rain-water) or from the chalk itself. Not only do worms aid indirectly in the chemical disintegration of rocks, but there is good reason to believe that they likewi e act in a direct and mechanical manner on tho sn1aller particles. All the species which swallow earth are furnished with giz7-ards; and these are lined with so thick a chitinous membrane, that Perrier speaks of it,* as "uno veri table armature." The gizzard is surrounded by powerful transverse muscle·, which, according to Claparede, are about ten times as thiclc as the longitudinal ones ; and Perrier saw them contracting energetically. Worms belonging to one genus, Dia-aster, have two distinct but quite similar gizzards; and in another genus, Moniligaster, the second gjzzard consists of four poucbes, one succeeding the other, so that it may almost be said to have five gizzards.t In tbe same * 'Archives do Zoolog. cxper.' tom. iii. 1874, p. 409. t 'Nouvelles Archives dn Museum,' tom. viii. 1872, p. 95, 131. CIIAP. V. AND DENUDATION. 247 manner as gallinaceous and struthious bird~ swallow stones to aid in the trituration of their food, so it appears to be with terricolous worms. ':rhe gizzanls of thirty-eight of our common worms were opened, and in twentyfive of them s1nall stones or grains of sand. sometimes together with the hard calcareous concretions formed within tho anterior calciferous glands, were found, and in two others concretions alone. In the gizzards of the rernaining worms there were no stones ; but some of these were not real exceptions, as the gizzards were opened late in the autumn, when the worms had ceased to feed and their gizzards were quite empty.''* When worms make their burrows throurrh b earth abounding with little stones, no doubt many will be unavoidably swalJowod ; but it must not be supposed that this fact accounts for the frequency with which stones and sand are found in their gizzards. For beads of glass and fragments of brick and of hard tiles were scattered over the surface "' Morren, in speaking of the earth in the alimentary cann.l~; of worms, says, "prrusevc cum lapilliH commixtam vidi:" 'De Lumbrici tcrrcstris,' &c., 1829, p. 16. |
