Arenicola marina 99 



THE CLEANSING OF THE SAND BY THE AGENCY OF ARENICOLA. The 

 lug worm burrows to a depth of two feet or more, 1 swallowing sand 

 as it goes (p. 64). Some, probably the greater part, of the organic 

 matter in the sand ingested is removed during its passage through 

 the alimentary canal of the worm, and the sand is eventually dis- 

 charged, in the form of a " casting," on the surface, where it is 

 subjected to further purification by the action of the air and water. 

 This worm performs great service in regard to " the cleansing of 

 the littoral," :! taking a prominent share in bringing about the 

 removal of substances which, if left to accumulate, would become 

 objectionable. When it is borne in mind how great are the numbers 

 of castings visible on many of our beaches, that they are renewed 

 twice each day as the tide falls, and that probably the worms carry 

 on similar operations during the intervals in which they are covered 

 by the sea, the magnitude of the collective work done by lug worms 

 becomes evident. 



Dr. Davison 3 estimated the amount of sand brought to the 

 surface by lugworms on the Holy Island sands. After finding the 

 average number of castings on nineteen measured areas to be 82,423 

 per acre, he weighed about fifty castings, and from the results calcu- 

 lated that the average amount of sand brought up to the surface 

 each year on these areas was about 1,911 tons per acre, which, if 

 spread evenly, would form a layer about thirteen inches in depth. 

 Taking two feet as the average depth to which the worms descend, 

 the sand in which they live would be passed through their alimentary 

 canal once in every twenty-two months. 



The writer (1904) made similar observations near Musselburgh 

 and Portobello, Firth of Forth, on the beaches of both of which lug- 

 worms are abundant. In the former locality the castings varied in 

 number from twelve to fifteen per square yard, and were evidently 

 formed by large worms ; near Portobello the castings were more 

 numerous 34 to 38 per square yard, but much smaller, so that the 

 amount of sand brought up was about the same in both cases, and 

 was estimated to be about 3,700 tons per acre annually, equivalent 

 to a layer about two feet in thickness. 



THE USE OF ARENICOLA MARINA FOR BAIT. A. marina is the best 

 known worm of our shores by reason of its extensive employment 



1 In cold or stormy weather the worms seem to burrow more deeply. 



2 J. Hornell, Journ. Mar. Zool., i (1894), p. 27. 



3 Geol. Mag., n.s., Dec. Ill, viii (1891), p. 489. 



H 2 



