THE INTERNAL ECONOMY OF THE SEA 



ing and stuffing material and as a covering for 

 Italian flasks of wine or oil. Mixed with this 

 Zostera are the seaweeds proper, attached but with- 

 out true roots, enlivening the grass-green with 

 beautiful reds, browns, and olives. Farther out 

 the seaweed vegetation thins, until it disappears at a 

 depth of about twenty-five fathoms. It is a crowded 

 vegetative area, able to support a crowded animal 

 life ; the waving sea -grass is often as thick as the 

 stems in a cornfield, and Professor Petersen notes 

 that the total annual yield in Danish waters is 

 about four times the quantity of hay produced in a 

 year in Denmark. The Zostera is already used for 

 fodder, for paper-making, and in other ways but 

 sea-grass is a difficult harvest to reap, and perhaps its 

 greatest value is the indirect one, that it forms a 

 basal food supply for animals on which many food 

 fishes mostly depend. For what Professor Petersen 

 and his colleagues have discovered is that the 

 surface of the mud (or clay farther from shore) is 

 covered by a thin layer of detritus of high nutritive 

 quality, and that this is mainly produced by frag- 

 ments of sea-grass and littoral seaweeds, the down- 

 ward sinking surface animalcules counting for little. 

 Examination of the stomach contents of common 

 non-predatory animals like oysters shows that they 

 feed very largely on the vegetable dust of the sea. 

 The circulation of materials is very interesting. 

 To make a pound of cod requires 10 Ib. of whelk or 

 buckie ; to make a pound of buckie requires 10 Ib. of 

 worms ; to make a pound of worm requires 10 Ib. 

 of vegetable matter, which may be given in the 



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