1911] Kofoid: Self-closing Planldon Net. 325 



in all respects so that no plankton can enter while the net is 

 closed, a feature obviously requiring finer adjustment in nets 

 using the finest (no. 20) silks than in those with bags of coarser 

 mesh, (4) sufficient weight to insure a measurable control of 

 level of operation in towing, and (5) an orifice free from im- 

 peding structures. These desiderata have been secured in the 

 net here described (pis. 22 to 25) which is the result of many 

 tentative designs and is an improved form of the model first 

 constructed. 



ACKNOWLEDGMENTS 



The general type of net adopted is one suggested to me in 

 correspondence by my friend, Dr. Gr. Herbert Fowler, of Aspley 

 Guise, Bedfordshire, England, of the "Research" Expedition. 

 I am greatly indebted to the San Diego Marine Biological Asso- 

 ciation, and its scientific director. Professor W. E. Ritter, for 

 their continued interest in the project, and for the aid which 

 carried it through the expensive experimental stage. In the 

 original designing of the net I have had the valuable aid of ^Ir. 

 Val Arntzen, expert mechanician at the University of California, 

 and in the final designing, pattern-making, and solution of 

 mechanical difficulties of construction, I have had the invaluable 

 assistance of Mr. Robert Baker of the Baker Machine Company 

 of San Diego. I am also indebted to ]\Ir. E. L. Michael of the 

 Biological Station at La Jolla, who has had considerable experi- 

 ence in the vise of the first model of the net, for suggestions and 

 criticisms. 



The net here described was first built in 1908. In 1909-10 

 a second and improved model was constructed for the Prince 

 of Monaco for the exhibit of oceanographic instruments in the 

 Musee Oceanographique at ]\Ionaco, Princepaute de Monaco. 

 The description which follows pertains, in the main, to this net. 



GENERAL DESCRIPTION 

 The net in general plan is a jointed-ring net with circular 

 opening, operated by messengers which release the semicircular 

 laterally hinged jaws actuated by springs. The frame is very 

 heavy and its weight may be increased by the addition of special 

 weights below. The trips are held in place by springs. The 



