316 University of California PuNications in Zoology. [Vol.8 



the net a sliding sheet of copper. The chains which controlled 

 the movement of the curtain were also dispensed with. The 

 net was otherwise opened and closed as in the original model, 

 and is reported to have worked with certainty and to have given 

 satisfactory results. 



The Tanner self-closing net, first described by Agassiz (1892), 

 and later, also in an improved form, by Tanner (1893, 1894), 

 is designed for "intermediate towing," which in action is prac- 

 tically horizontal, since, b^' "veering and heaving in on the tow 

 line" the desired depth may be maintained. The depth at 

 which the net is operating is ascertained by the dredging quad- 

 rant. The net is lowered vertically while open and is then 

 towed at the desired depth and closed by messenger after return 

 of cable to the vertical position. The closure is by weights 

 which draw a puckering string about the middle of the bag. 

 The lower end will thus contain the catch made before closure. 

 In the earlier model the closing weights worked on guy ropes 

 running from the net ring to the terminal weight. In the later 

 model two lateral brass pipes were substituted for the ropes 

 and the weights slide down these. At the lower ends the pipes 

 are attached to an apron or vane which is supposed to prevent 

 the whirling of the net. 



In the hands of Mr. Agassiz and Captain Tanner this net 

 has given satisfactory results. The objections which may be 

 urged against it are that (1) the successful operation in inter- 

 mediate levels, i.e., while functioning as a horizontal net, requires 

 considerable speed and introduces some uncertainty as to the 

 level of its operation, (2) the net is open in descent and the 

 vortex about its rim may introduce some animals into the net, 

 (3) the open upper part of the bag of the net brings, during 

 ascent, considerable pressure to bear upon the region of closure, 

 tending to force the catch of the upper part of the bag into the 

 lower. Another objection, applicable especially to the first 

 model, is that the heavy weight attached to the tail of the net 

 to keep the guy ropes supporting the closing weights in place, 

 would tend to interfere with the mouth of the net taking a 

 position of maximum exposure to the water entering the net, 

 i.e., to keep it vertical, instead of oblique, during the horizontal 



