490 Charles Bmison — Work done hy Lobworms. 



of sand (called the Holy Island Sands) about three miles wide, 

 which is laid bare by the sea a few hours after high-water, and is 

 then seen to be thickly studded with castings formed by lobworms. 

 In any one spot, the castings seem to be scattered with a fair 

 approach to uniformity, but patches of sand, apparently not differing 

 from the rest, occur in places without any castings. When the 

 surface is covered with broken shells, they are also rare or altogether 

 absent, unless the sand is much ripple-marked, and then the shells 

 collect in the hollows, while castings are common on the inter- 

 vening ridges. A few observations were also made in the two bays 

 on the north side of the island, but here the beach is more exposed, 

 and consequently the castings, though hardly less numerous, had 

 lost more from the action of the rougher sea. 



It will be obvious that the second, but more accurate, of Mr. 

 Darwin's methods was the only one that could be followed with 

 profit in the present case. In several places where the castings 

 were uniformly scattered, I marked off spaces bounded by straight 

 lines, some of them roughly square, but the majority triangular iu 

 form. Within these spaces I counted all the castings that had been 

 thrown up, with one exception, either about or after the time of low- 

 tide, and from six of them filled wide-mouthed jars with castings, 

 which were afterwards thoroughly dried and weighed. 



Number of castings in a given area. — On the Holy Island Sands, 

 I counted the number of castings in nineteen measured areas, all but 

 one within the square mile, bounded on two sides by the Snook and 

 the west coast of the island. The smallest of these areas contained 

 2,679 square inches, the largest 17,278 ; the average being 6,268 

 square inches, or a little less than five square yards. In order to 

 compare the results with one another, and with those given by 

 Mr. Darwin, I have calculated in each case the equivalent number 

 of castings per acre. The smallest number so found is 39,935, the 

 largest 203,272. In both these cases the castings were fairly large. 

 In two other areas, where the castings were the largest I have seen, 

 the numbers are 52,568 and 70,372. Taking all the 19 areas together, 

 the average number of castings is 82,423 per acre, or more than fifty 

 million per square mile. 



On the north coast of the island there are two bays in which 

 patches of sand occur. In each of these I counted the number of 

 castings in three measured areas, but the numbers here given may be 

 too small, for the castings had obviously lost much by the rougher 

 sea, and it is possible that some were altogether obliterated. In 

 Caves Haven, the more westerly of the two bays, the average area 

 measured was 10,162 square inches ; and the numbers of castings per 

 acre were 86,344, 75,345 and 50,036, the average of these being 

 70,575 per acre. In the other bay, that to the west of Emanuel 

 Head, the average area measured was 5,714 square inches, and the 

 numbers of castings per acie 227,177, 65,584 and 62,114, the average 

 being 94,466 per acre. The castings in the first of the last three 

 areas were however small. 



Weight of the castings in a given area, — Castings were collected 



