UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 8, No. 8, pp. 311-348, pis. 22-25 November 18, 1911 



ON A SELF-CLOSING PLANKTON NET FOR 

 HORIZONTAL TOWING 



BY 

 CHAELES ATWOOD KOFOID 



(Contribution from the Laboratory of the Marine Biological Association of San Diego) 



A prime desideratum for marine exploration has long been 

 a self-closing plankton net for horizontal towing. This type 

 of apparatus is especially needed for the investigation of the 

 vertical distribution of pelagic organisms, is indispensable for 

 the detection and analysis of their vertical migrations, and is 

 a necessity for the study of distribution and of migrations in 

 stratified waters where abrupt changes in temperature, salinity, 

 and plankton content may occur within a short vertical distance. 



The evidence of such stratification brought to light by the 

 investigations of the Biological Station at La Jolla (see McEwen, 

 1910) and the plan of this enterprise to conduct a systematic 

 regime of work upon the plankton (see Ritter, 1905) have made 

 necessary a survey of existing models of self-closing plankton 

 nets, with the result that it seemed necessary that a net for 

 horizontal towing would have to be devised especially for this 

 work. A brief historical resume will outline the development 

 of this line of apparatus and also serve to indicate the limitations 

 and defects which have been, or may be, attributed to the various 

 patterns hitherto employed for submarine investigations of the 

 plankton. 



HISTORICAL DISCUSSION 



The Sigsbee (1880) gravitating trap appears to be the first 

 self-closing instrument devised for plankton collecting in deep 

 water. It is a small sieve operating vertically, clamped upon 



