^^11] Kofoid: Self-closing Plankton Net. 313 



or oblique towing in shallow waters only, and was opened and 

 closed (by constriction) with a special rope for the purpose. 

 The two lines would inevitably become entangled in use at any 

 considerable depth, and perfect closure would be difficult to 

 secure and maintain. 



Pouchet and Chabry (1887) describe a net, used (?) at 

 Concarneau after experiments on the "Hirondelle" with the 

 Chun net, which is an adaptation of the Pavesi model. Two 

 heavy semicircular jaws turning on a vertical axis which tra- 

 verses the mouth of the net are slipped down this axis by the 

 action of messengers, a curved slot in the surface of the axis 

 guiding each jaw through an opening and closing movement 

 of 90°. Details as to messengers, trips, and control of the 

 movement of the arms are wholly lacking in both the description 

 and figures, and the further development of the model seems 

 to have been abandoned. 



Later the Prince of Monaco (1887) describes an improved 

 form of closing-net made b.y Dumaige, the original of which 

 he ascribes to de Guerne. Both the original de Guerne net and 

 the improved form differ from the Pavesi net, upon which they 

 also are modeled, in having a vertical axis bearing the coiled 

 spring which traverses the opening of the net, and in being 

 both opened and closed by messenger. The axis is an obstacle 

 to some forms of organisms entering the net and it is evident 

 that the closure cannot be complete in the nets as figured. No 

 further use or improvements in this net seem to have been made 

 in the later campaigns of the "Hirondelle" and her successors, 

 and the author later (1889a) describes the closing action of the 

 half-ring as inconstant and the closure as sometimes delayed till 

 the net is removed from the water. 



In the same paper (1887) a modified form of the Chun- 

 Petersen net then in use by Professor Chun at the Naples Station 

 is also described and figured. The modifications pertain to 

 minor matters of the form of the spiral thread on the axle, the 

 propeller, and the attachment of the net. The principles of 

 operation by propeller and of vertical action remain unchanged. 

 The Chun-Petersen net described by Chun (1888, 1903) is 

 a vertical net which is lowered closed, opened by the action of 



