314 University of California Publications in Zoology. [Vol. 8 



a propeller, and, after a period of towing, is later closed by 

 continued action of the propeller and the release of one set of 

 connections between the net and the cable, and the transfer 

 of its weight to another set, which closes the jaws. This net 

 has been criticized by the Prince of Monaco (1889a), who re- 

 garded the action of the propeller as so uncertain that the depth 

 at w^hich the net functioned could not be established, since the 

 surge of the ship, irregularities in heaving out and hauling in 

 the cable, and entanglement of siphonophores and medusae upon 

 the propeller would all tend to modify, or impede the releasing 

 action of the propeller, and render uncertain the time and levels 

 in which the net was in operation. He also regarded the closure 

 as incomplete, a defect noted by Chun (1889) himself, which 

 has, however, been remedied in later models of the net. Later 

 Agassiz (1888b, 1892) criticizes the net on the grounds of its 

 imperfect closure, and Ilensen (1895) regards even the improved 

 form as still defective. In any event some uncertainty as to 

 the time and level at which any closing-net, which is actuated 

 by a propeller, is really in operation, must always remain. 



Hoyle's (1889) deep-sea towing net is built on a unique 

 pattern for operation while towing with the cable in oblique 

 position. The net is operated by messengers which release ropes 

 attached to the hinged semicircles which constitute the rim of 

 the net. The strain of towing is relied upon to keep the net 

 closed both in descent, and, after closing, during ascent. It is 

 obvious that irregularities in the tension upon the towing cable 

 due to surge of the ship or changes in speed of reeling engine 

 or ship will endanger the continuity and certainty of closure 

 of the jaws of the net both during descent and ascent. This 

 net does not seem to have been adopted elsewhere. 



The next considerable step in advance was made by the 

 Prince of Monaco's (1889a, 1889b, see also Marenzeller, 1891, and 

 Richard, 1902, 1910) curtain net. This is built upon an entirely 

 new principle and was adopted after partial tests at sea of the 

 net of the Pavesi (1883) type as modified by de Guerne and 

 later by Dumaige (see Monaco, 1887), and after tests of a net 

 of the Chun-Petersen type. The net is devised for horizontal 

 towing, at the end of a vertical cable. The cable with terminal 



