184 THE HARMONIES OF NATURE. 



feed on decaying vegetable matter, of the Birgus or robber-crab, 

 which delights in the sweet kernel of the cocoanut, of the 

 water-fleas, which feast on the tender fronds of the green sea- 

 weeds, arid of a few other species, the crustaceans are eminently 

 carnivorous. Their amazing numbers, their voracity, their 

 powerful claws render them the most formidable enemies both 

 of the weaker among their own class and of all the lower aquatic 

 animals. Even the fishes and cetaceans are not exempt from 

 their attacks ; and as the whale, the carp, the sturgeon, the 

 shark, the perch have each of them their peculiar crustacean 

 parasites, it can easily be imagined how large the number of the 

 still unknown species must be which feast on tha,t vast host of 

 fishes that has never yet been accurately examined. Some bore 

 or eat holes into the skin of their victims, others fasten on their 

 gills, and many settle in their entrails ; where, no doubt, they 

 lead a more pleasant life than that which, through their agency, 

 falls to the share of their involuntary entertainers. 



On the other hand, the crustaceans constitute a great part of 

 the food as well of the sea-stars, sea-urchins, annelides, and 

 many of the molluscs, as also of the fishes and sea-birds ; and as 

 they are found of all sizes, from microscopical smallness to a 

 weight of several pounds, they are able to satisfy the wants of a 

 great variety of animals. 



Man also is indebted to the crustaceans for many a savoury 

 morsel; and while the Europeans enjoy their lobsters, crayfish, 

 and shrimps, the islanders of the torrid zone not only feed upon 

 many marine crustaceans, but also upon the fat of the long- 

 tailed Birgus and the white flesh of the land-crab. The injuries 

 inflicted upon mankind by the crustaceans are certainly inferior 

 to their services, though several species (Chelura terebrans, 

 Limnoria terebrans) are great destroyers of submerged timber, 

 and others are said to be poisonous. 



A carnivorous race exposed to so many persecutions necessarily 

 requires to be well furnished with the means of attack and defence. 

 Thus in all the higher crustaceans we find, with rare exceptions, 

 the anterior thoracic extremities terminating in pincers of greater 

 or less strength, armed with teeth and sharp hooks which give 

 them increased powers of prehension. Generally only the first 

 pair of legs is converted into these formidable weapons, but in 

 the crayfish the second and third pair of feet are likewise pro- 



