CHAPTER XXIII 

 COPEPODA 



By C. DWIGHT MARSH 



United States Department of Agriculture 



Of all animals encountered in fresh water, perhaps none are 

 more likely to arouse interest than the Copepoda. Wliilc many of 

 them are large enough to be seen and watched with the naked 

 eye, yet they are so small that a microscope is needed to get a 

 clear understanding of their form and structure. In company with 

 the Cladocera, they are almost universally distributed, and can be 

 collected in nearly any body of water. Unlike the Cladocera, 

 which show many erratic and bizarre species, the Copepoda are 

 graceful and symmetrical in their forms, with a beauty of structure 

 that is very attractive to the amateur student. Some are wonder- 

 fully transparent, while others are strikingl}' and in some cases 

 gorgeously colored. 



Copepoda have been studied ever since the microscope was first 

 used. It is said that the first mention of these animals was made 

 by Stephen Blankaart in 1688. 0. F. IMuller in 1785 is credited 

 with having given the first scientific description of this group. 

 In 1820 Jurine published his famous ''Histoire des monocles qui se 

 trouve aux environs de Geneve." Some of the species which he 

 described are still recognized as valid, largely, however. b\- the 

 courtesy of succeeding writers; for Jurine made his distinctions on 

 insufficient grounds like color, and it is only through his figures 

 that one can conjecture what species he had in hand. No really 

 serious study of this group was made until the middle of the nine- 

 teenth century, when the publication of Baird's "Natural IIistor>- 

 of the British Entomostraca " in 1850 and the various papers ol 

 Claus a few years later were the beginning of exact work on these 

 forms. The work of Claus was of first importance. In Sorih 

 America articles were published recrardin- some forms in the early 

 part of the century, but nothing recognizable appeared until S. A. 



74t 



