THE ECONOMIC HISTORY OF COPEPODS 



By Arthur Willey 

 Professor of Zoology, McGill University, Montreal, Canada 



It is perhaps superfluous to repeat the time-honored state- 

 ment that the ultimate object of the scientific study of organ- 

 isms is to give precision to the facts of common observation, 

 to extend biological knowledge, and to apply it when oppor- 

 tunity offers. No single line of investigation is competent to 

 supply all the information necessary before we can undertake 

 to interfere with the course of nature and with the custom of 

 fishery. It is hardly a fair question to ask what is the use of 

 a particular contribution, because new and striking develop- 

 ments may arise from the most unexpected quarters. This 

 paper has to deal briefly with one small branch of the subject, 

 but it is one which has been cultivated much in our own time. 



Crustaceans were called Malacostraca by Aristotle who 

 meant to include under that term only the higher forms (crabs, 

 crayfishes, shrimps, prawns, langoustes and lobsters) whose 

 shell has to be crushed, in contrast with the Ostracoderma or 

 shell-bearing mollusks whose shell must be shattered to get at 

 the soft parts. In more recent classification crustaceans com- 

 prise three principal subdivisions, beginning with those of small 

 size, then passing to those of larger average dimensions, and 

 finally the largest: Entomostraca (water-fleas and copepods) ; 

 Arthrostraca (sand-hoppers, scuds, and fish-lice) ; and Mala- 

 costraca, still employed in the Aristotelian sense. 



The name of the order Entomostraca was introduced from 

 Denmark in 1785, but some of the members of it had been seen 

 in the 17th century, in the early days of the invention of the 

 microscope. One feature which nearly all of them possess in 

 common is a single median eye. It may be divided by notches 

 into three parts, in which case it presents a tribolate appearance; 

 and the parts may, in rare instances, become separated, but the 

 single eye is typical of the group. On account of this one-eye 



