PLANKTONIC STUDIES. 577 



series of observations for a later and more detailed work. But since, 

 to my regret, I am compelled to decidedlj' contradict the far-reacliing 

 assertions made by Hensen (22), it is only to justify and prove these 

 that I refer to my extended experience of many years. I believe I do 

 not err in the assumption that among living naturalists I am one of 

 those who by extensive investigation on the spot have become most 

 thoroughly acquainted with the conditions of the plankton and have 

 worked deepest into these intricate problems of marine biology. If I 

 had not for so many years hud these continually in mind, and at each 

 new visit to the sea begun them anew, I would not dare to defend with 

 such determination the assertions expressed in the following pages. 



III.— CHOROLOGICAL TERMINOLOGY. 



The science of the distribution and division of organic life in the sea 

 (marine chorology) has in the last decade made astonishing progress. 

 Still this new branch of biology stands far behind the closely related 

 terrestrial chorology, the topography and geography of land-dwelling 

 organisms. We have as yet no single work which treats distinctly 

 and comprehensively of the chorology of marine plants and animals in 

 a manner similar to Griesbach's <' Vegetation of the Earth" (1872) for 

 the land jilants, and Wallace's "Geogra])hical Distribution of Animals" 

 (187G) for the land animals. 



How much there is still to be done is shown by the fact that not one 

 of the simplest fundamental conceptions of marine chorology has yet 

 been established. For example, the most important conception of one 

 subject, that of the pelagic fauna and flora, is now employed in three 

 different senses. Originally, and through several decades, this term 

 was used only in the sense in which Johannes Miiller used it, for ani- 

 mals and plants which are found swimming at the surface of the sea. 

 Then the term was extended to all the different animals and plants 

 which are found at the surface of fresh- water basins. It was so used, 

 for example, by A, Weismann in his lecture upon " the animal life at 

 the sea-bottom" (1877), in which he "distinguishes the animal world 

 living on the shore from the 'pelagic or oceanic company living in the 

 open sea.'" To a third quite different meaning has the conception of 

 the pelagic living world been widened by Chun (1887), who extends it 

 from the surface of the ocean down to the greatest depths (15, p. 45). 

 In this sense the conception of the pelagic organisms practically agrees 

 with the "plankton" of Hensen. 



Errors have already arisen from the varied use of such a funda- 

 mental conception, and it seems necessary to attempt to clear this up, 

 and to establish at least the most important fundamental conception 

 of marine chorology. In the use of words I will, as far as possible, 

 conform to the usage of the better authors. 

 H. Mis. 113 37 



