56 LIFE IX THE SEA [PART I 



apparatus on board the Challenger in 1873-6 an enormous advance 

 was made in our knowledge of marine life. 



When to the creatures captured by the dredge and the apparatus 

 of the fishermen were added those obtained by the tow-net it 

 became possible to devise a new grouping of the organisms found 

 in the sea. In 1887 Victor Hensen published the results of a voyage 

 of exploration in the North Sea and Atlantic Ocean, and in this, 

 now classical, memoir ( Ueber die Bestimmung des Planktons oder 

 des im Meere triehenden Materials an Pflanzen und Thieren) he used 

 for the first time the now familar word Plankton, replacing by it 

 the older " Auftrieb " of Johannes Muller. In 1890 Ernst Haeckel 

 published the famous Plankton- Studien, a memoir largely 

 controversial in treatment, but containing the resume of a wide 

 experience in the investigation of the plankton of the sea. In 

 this paper Haeckel invented a number of new terms to be used in 

 such discussions, terms which have not all met with general 

 acceptance, but some of which have been adopted. In the 

 Plankton- Studien Haeckel proposed to distinguish the animals 

 which are caught in the tow-nets from those which are obtained 

 generally by other means. If we take a broad survey of organisms 

 found in the sea and consider their habit of life we will find that 

 all can be grouped in three great categories. There are first of all 

 ^those which by reason of their minute size and feeble powers of 

 locomotion are carried about passively in the sea by tides and 

 currents. These are they which are caught in the tow-nets, which 

 Miiller called the Auftrieb, and Hensen the Plankton. Then 

 there are those animals and plants which can be taken by means 

 of the dredge or gathered on the foreshore. Sea-weeds, molluscs, 

 starfishes and their allies, zoophytes and most Crustacea belong to 

 this group. They are organisms which, like the sea- weeds and 

 the zoophytes, live attached to the sea bottom, or like the molluscs 

 and echinoderms live there more or less permanently and make 

 few or unimportant migrations. These form the " Benthos " and 

 Edward Forbes' classification included only such creatures. Then 

 opposed to both these categories are the numerous class of animals 

 which roam about over comparatively wide areas of sea. Such 

 are the fishes, the marine mammalia and some molluscs and 

 Crustacea. For the reception of these animals Haeckel, to whom 



