PLANKTON INVESTIGATIONS ' 



1 he investigation of the occurrence and distribution of the forms of life, which 

 together constitute the plankton floating in the sea, has made great progress 

 during the first two years of the common international work. Plankton-nets have 

 been used almost regularly at every station during the seasonal cruises, and both 

 the surface and the deeper layers of the sea have been investigated. Horizontal 

 as well as vertical hauls have been made; in order to separate the plankton-forms 

 dwelling in the different layers of water from one another, closing nets of various 

 construction have been used. In order also to obtain the smaller forms, especially 

 those of the vegetable plankton, the finer qualities of silk gauze have been em- 

 ployed. Plankton-nets of coarser material (cheese-cloth etc.) have also been used, 

 especially on the surface, to catch representatives of the larger forms of the 

 plankton, with which, as is well known, the eggs and fry of fishes are reckoned. 



The extraordinarily rich material, collected in this manner, has been worked 

 out after each seasonal cruise by the specialists of the various countries with 

 perseverance and conscientiousness; almost all the species could be determined, 

 and detailed lists of the forms found, with indications of their occurrence and 

 abundance at the various stations, could be forwarded quarterly to the Bureau 

 and published in the Bulletin. The tables for the first two years fill abut 350 

 closely printed pages in quarto, and constitute a truly comprehensive enumeration 

 of the commoner plakton-forms as well as of very many rarer forms of the North- 

 European seas, with a statement of the fishing-places and the abundance estimated 

 by the different naturalists. The material could in general be mastered in this 

 way, when it was only necessary to limit the determinations to estimates of the abund- 

 ance and when the desirability of a more exact determination of the abundance 

 had not been agreed upon. One of the plankton investigators (Dr. C. Apstein, Kiel) 

 counted the numbers each time, basing his calculation on a sq. met. and from the 

 figures thus obtained, calculating the quantity of the organisms in one cub. met. From 

 these latter numbers the frequency was then determined by means of a previously 

 constructed table. By many of the plankton investigators, however, the total 

 volume of the catch was given. 



Apart from the seasonal cruises, plankton was also collected from the sea in 

 several of the participating countries, as follows: 

 1°. Surface-plankton, by many steamers trading regularly across the North Sea 



and Atlantic Ocean. 

 2°. Surface and deep-water plankton, by numerous boats stationed at fixed points 



(light-ships). 



The results obtained from the elaboration of this material, have only been 

 partly published as yet, (Prof. P. T. Clkve prepared lists of the plankton collected 

 by numerous steamers in the North Sea for the Bulletins of 1902 — 03 and 1903 — 04); 



I Part I and 2 are translated from the German bv Dr. H. M. Kyle. 



