72 THE CRUSTACEA 



before the affinity of the two groups was recognised. Linnaeus 

 included some free-living Copepods in his genus Monociilus, among 

 the Crustacea, but some of the parasites were placed under " Vermes 

 mollusca " in the genus Lernaea, and others among the " Zoophyta " 

 in the genus rennatula. 0. F. M tiller's great work on the 

 " Entomostraca " marks the beginning of a new ejDOch in the study 

 of the group. The genera Cyclops, Caligus, and Argulns were 

 established by Miiller, besides two others based on larval stages, 

 one of which, the Nauplms, still bears the name given to it by 

 Miiller. Jurine's Histoire des Monocles (1820) is noteworthy, 

 among much else, for the description of the larval metamorphosis 

 of Cyclops, the earlier stages of which had been seen long before by 

 Leeuwenhoek and de Geer. Although an affinity between the 

 highly modified Lernaeidae and the less- specialised parasites like 

 Caligus was suggested, more or less definitely, by Oken, Lamarck, 

 and others, it was not until von Nordmann's researches (1832) 

 threw light on their development that the Lernaeidae and their 

 allies were definitely accepted as Crustacea. Li most systems of 

 classification, however, the parasites were more or less Avidely 

 separated from the free-living forms, and hy Milne-Edwards they 

 were even placed alongside of the Pyenogonida in a different sub- 

 class. Milne-Edwards introduced the name Copepoda for the 

 free-living forms alone. Zenker, in 1854, seems to have been the 

 first to associate together free-living and parasitic forms under the 

 name Entomostraca. Modern conceptions of the morphology and 

 classification of the Copepoda are largely based upon the long series 

 of highly important memoirs (1857-1895) by C. Claus. Among 

 faunistic workers, J. D. Dana, H. Kroyer, Steenstrup and Liitken, 

 van Beneden, and Brady, may be specially mentioned. Li more 

 recent years, W. Giesbrecht, in his splendid monograph of the 

 pelagic Copepoda and other imjiortant works, has given a new 

 aspect to the problem of classification, by showing that the 

 parasitic habit has been acquired not once but many times in the 

 evolution of the group, and that the line of division, maintained 

 even in Claus's classification, between free -living and parasitic 

 forms must be abandoned. Hansen's fine monograph of the 

 Choniostomatidae has raised that family, previously obscure, to the 

 position of one of the best known among the parasitic gronps. 

 Finally, G. 0. Sars's work on the Copepoda of Norway, now in 

 course of publication, is especially important as regards the bottom - 

 living marine forms, which in recent years have been less studied 

 than the more easily collected pelagic species. The small group of 

 the Branchiura, associated by the older authors with the parasitic 

 Copepoda, were removed by Zenker to the Branchiopoda. Claus 

 restored them to the Copepoda, and his arrangement is followed 

 here, but in view of the important differences which separate them 



