OCR Text |
Show 120 HABITS OF WOHMS. CHAP. II. tho movements were twice as great. These observations were maJe by rny son Horace, who will hereafter publi h an account of tho movements of this stone during successive wet and dry seasons, and of the effects of its being undermined by worms. Now when the ground swells, if it be penetrated l>y cylindrical holes, such as worm-burrow~, their walls will tend to yield and be pre secl inwards; and tl1e yielding will be greater in the deeper parts (supposing tho whole to be equally moistened) from the greater weight of the superincumbent soil which h:1s to be raised, than in the parts ncar the ~:;nrface. When the ground dries, the walls will shrink a little and the burrows will be a little enlarged. Their enlargement, however, through the lateral contraction of the a-round will not be favoured, but rather op- o ' posed, by the weight of the superincumbent soil. Distribut£on ~f Worms.--Earth-worms arc found in all parts of the world, anJ orne of the genera h~ve an enormous range.* They inhabit the most isolated islandf:l ; they * Perrier, 'Archives do Zoolog. exp61'.' tom. 3, p. 378, 1874. CnAP. II. THEIR WIDE DISTRIBUTION. 121 abound in Iceland, and are known to exi t in tho vV est Indies, St. liel0na, Madagascar, New Caleclonia and Tahiti. In the Antarctic region , worms from Kerguelen Land have been described Ly Ray Lankester; and I found them in the Falkland Islands. IIow they reach such isolateJ. island i at pre out quite unknown. They are easily killed by salt-water, and it docs not appear probable that young worms or their egg-capsule could be carried in earth adllering to the feet or beaks of land-birds. Moreover Kerguelen Land is not now inhabited by any land-bird. In this volume we are chiefly concerned with the earth cast up by worm , and l have gleaneJ. a few facts on this subject with re pect to distant lands. Worms throw up plenty of castings in the United States. In Veneznela, castings, probably ejected by species of U rocbreta, are common iu the gardens and fields, but not in the forests, as I hear from Dr. Ernst of naracas. II e collected 15 () castings from the court-yard of his house, havi_ng an area of 200 square yards. They varied in bulk fron1 half a cubic centirueter to five cubic centimeters, and were on an average |