3911] Kofoid: Self-closing Plankton Net. 335 



Michael, 1911) with very satisfactory results in depths of 5 to 

 550 fathoms in explorations at sea in the Pacific off San Diego 

 in the "Alexander Agassiz, " a vessel of twenty tons, seventy 

 feet in length. 



The main objection to the net has been its great weight, a 

 difficulty partly removed in the somewhat lighter model here 

 described. The determination of the tension of the springs for 

 closure at given depths has taken some time, but when once 

 determined empirically for certain intervals the tensions for 

 intermediate depths may be approximated without trial. 



The net, especially with the finer grades of silk in the bag, 

 is not devised for rapid towing, nor for large, actively moving 

 animals such as the larger fishes and cephalopods. It does, 

 however, take the very alert and actively moving Sagitta in 

 large numbers and its catches in general exhibit a wide range 

 of plankton forms from Salpa, Schizopoda and other plankton 

 crustaceans, to the smaller forms. It should be possible to con- 

 struct a net on this plan with large orifice with a bag of coarse 

 mesh for the larger and more active forms. Such a net would 

 have the advantage of an entire absence of all disturbing bars, 

 ropes, cables, etc., in front of the opening. 



The advantages which the net here described possesses over 

 other models devised for deep-sea work are as follows : 



1. A method of opening the net and closing it again at any 

 desired level in the sea under complete control of the operator 

 and free from interference by outside conditions. 



2. Perfect and continuous closure of the net during descent 

 and ascent of the apparatus, completely preventing the entrance 

 of organisms except when the net is opened by the operator and 

 preventing their escape after the net is closed. 



3. The possibility of horizontal towing which makes feasible 

 the more precise exploration of stratified waters, and the vertical 

 migrations of pelagic organisms. 



4. An opening free from interfering structures which tend to 

 ward of¥ the more active pelagic animals. 



Zoological Laboratory, JJniversity of California. 

 Transmitted October 2, 1911. 



