CHAPTEE I 



CRUSTACEA GENERAL OIIGANISATIOX 



The Crustacea are almost exclusively aquatic aninials, and they 

 play a part in the waters of the world closely parallel to that 

 which insects play on land. The majority are free-living, and 

 gain their sustenance either as vegetable-feeders or by preying 

 upon other animals, but a great number are scavengers, picking 

 clean the carcasses and refuse that litter the ocean, just as 

 maggots and other insects rid the land of its dead cumber. 

 Similar to insects also is the great abundarfce of individuals 

 which represent many of the species, especially in the colder 

 seas, and the naturalist in the Arctic or Antarctic oceans 

 has learnt to hang the carcasses of bears and seals over the side 

 of the boat for a few days in order to have them picked 

 absolutely clean by shoals of small Amphipods. It is said that 

 these creatures, when crowded sufficiently, will even attack 

 living fishes, and by sheer press of numbers impede their escape 

 and devour them alive. Equally surprising are the shoals of 

 minute Copepods which may discolour the ocean for many miles, 

 an appearance w^ell known to fishermen, who take profitable toll 

 of the fishes that follow in their wake. Despite this massing 

 together we look in vain for any elaborate social economy, or for 

 the development of complex instincts among Crustacea, such as 

 excite our admiration in many insects, and though many a crab 

 or lobster is sufficiently uncanny in appearance to suggest 

 unearthly wisdom, he keeps his intelligence rigidly to himself, 

 encased in the impenetrable reserve of his armour and vindicated 

 by the most powerful of pincers. It is chiefly in the variety 

 of structure and in the multifarious pliases of life-history that 



