OF SOME COMMON MARINE ANIMALS. 253 



between tide-marks may become covered with a layer'of the little black dots 

 as if they had been thickly peppered over (fig.«4) ; and in favourable 

 localities the young mussels grow in a profusion which may cause their own 

 destruction. T have seen the rocks at Hilbre Island covered with a layer of 

 small mussels from a quarter to half an inch in length, which are so closely 

 placed as to be absolutely continuous, and to be tightly united to one another 

 by matted byssus fibres, while they have little or no attachment to the rock 

 beneath, the result being that in the first storm the waves roll up the sheets 

 of mussels and wash them ashore on the neighbouring sandy beaches in 

 masses as large as pillows and bolsters. 



In such sheets and masses I have counted from 80 to 100 mussels visible 

 on the surface of a square inch, and in the case of slightly older ones from 

 50 to GO (fig. 5), At the rate of 100 there would be about 129,000 in a 



Fig. 5. — Young mussels on Laminaria stem, nat. size. 



square yard, and there are very many such square yards around our coast. 

 No doubt the majority of these young mussels never grow to maturity. 

 They are killed by storms, smothered by their neighbours, or eaten by star- 

 fishes or by plaice and other fishes. In the latter case they are not lost as 

 a food matter, and even in the former their remains will be eaten by some- 

 thing which will indirectly feed man. Nothing is lost in the sea, and 

 everything ultimately in the metabolic cycle contributes to man's harvest. 



Dr. James Johnstone has estimated * that a Lancashire mussel bed may 

 have 1C,000 mussels to every square foot, and that the proteid contents of 

 the mussel flesh is comparable with that of a lean farm animal, while per 

 unit of area the mussel bed produces nearly a hundred times the amount of 

 flesh for food that is produced by cultivated land. The sea when cultivated, 



* ' Conditions of Life in the Sea,' Cambridge University Press, 190t~. 



