ON CRABS OF VARIOUS KINDS. 15 



the smaller and for the most part pelagic forms, which are not 

 sought by man for food, and the larger, amongst which are the 

 edible kinds. Every ocean and bay, from the Arctic to the 

 Antarctic region, teems with minute crustaceans, chiefly 

 copepods, which at various stages of growth form the food 

 of the younger fishes. It must not be supposed that their 

 small size is a barrier to their being preyed on by the most 

 gigantic inhabitants of the sea, since they form a large pro- 

 portion of the food of the right whale. In their larval stages 

 {Nauplii) they are fitted for the needs of the youngest 

 fishes, such as the cod and the turbot, just after the absorp- 

 tion of the yolk, and they are important links in the cycle 

 of marine life culminating in the fishes. Their ranks are 

 largely augmented by the larval stages of the sea-acorns 

 (Balani), which swarm in the inshore waters during the 

 spring months, and afterwards settle in dense multitudes to 

 form calcareous crusts on rocks, boats, stakes and stones in 

 the sea. The copepods occur during every month of the 

 year, and have been found by Dr George Murray and our- 

 selves to feed on diatoms, so that the links from plant to fishes 

 receive another illustration. These and the crowds of the 

 sessile-eyed crustaceans (such as Parathemisto in mid-winter) 

 provide an inexhaustible supply of food over which human 

 agency has no influence. Man in a minor way and with great 

 difficulty may protect his boats and ships, the piles of harbours 

 and other places of easy access, from the ravages of the 

 "gribble" (a minute crustacean called Limnoria), but he is 

 helpless in the case of floating or submerged timber. Nature 

 almost invariably carries out her own laws, and, as a rule, in 

 the sea these are beyond man's influence. 



Another group of crustaceans, viz., the Schizopods, are of 

 importance in most seas, even to a great depth, from their vast 

 abundance at certain seasons, and from their forming a 

 favourite food of valuable fishes such as the herring. For 

 instance in autumn the water near Crail, at the mouth of 

 the Forth, is occasionally crowded with Thysanoessa either 

 alone or accompanied by Boreophausia and Nyctiphanes — all 

 shrimp-like species of some size, and they may be stranded 



