CH. V] THE SEA-FISHERIES 103 



contain that they are worth some £200 a ton. The fresh water 

 mussels of our rivers (Anodonta and Unio) yield pearls which have 

 occasionally some value as gems ; and the common edible marine 

 mussel too furnishes pearls which had at one time a use in com- 

 merce. Some of the larger tropical mollusca are provided with a 

 byssus which is so large that its fibres are spun into cloth, which 

 is used in those parts of the earth where clothing is w^orn for its 

 primary purpose alone. The imperial purple of the Romans 

 was yielded by the molluscs Murex, Purpura and others ; and 

 the sepia of the artist is obtained from certain cuttle-fishes. Many 

 molluscs, both bivalves and univalves, are used as ornaments, and 

 from time immemorial the cowries {Cyprea) have served as a primi- 

 tive form of money. Coelenterates furnish few products of use to 

 man, but the precious red coral of commerce is a notable exception. 

 The whales and seals are, of course, very valuable, the former for 

 the oil and whalebone, and the latter for their skins. Many use- 

 ful products are yielded by parts of fishes caught primarily for food, 

 thus the swim-bladders of fishes are used to obtain isinglass, and 

 other parts of the piscine anatomy are employed for the manu- 

 facture of the coarser fish-glue. If no other use can be made of fish 

 offal it is converted into manure, and large quantities of starfishes 

 find this application in commerce, a use to which the rejectamenta 

 of our fish markets is also destined. Seaweeds are also made into 

 manure, and not so long ago all the bromine and iodine of 

 commerce were made from the kelp obtained by burning the 

 marine algae. 



Man has exploited the population of the sea from the earliest 

 times. Long before the origin of the arts and manufactures he 

 fished and hunted, and as the human animal increased in numbers 

 he became the most formidable eiiemy of those other animals with 

 which he at first competed on more or less equal terms. Man, the 

 hunter and sportsman, soon began to decimate the land, so that in 

 all civilised countries the larger and more slowly breeding animals 

 have become scarcer and scarcer, or have disappeared, as has been 

 the case with the elephants, bisons, deer and wolves. Even the 

 smaller and less valuable mammals like the hares, otters, badgers, 

 foxes and others are now rarities in densely populated countries. 

 The salmon would long ago have practically disappeared from the 



