1911] Kofoid: Self-closing Plankton Net. 329 



which is fastened by two small screws {s/} to the flat inner end 

 of the hub. The impelling force, however, for the movement of 

 the outer cjdinder comes in either jaw from the coiled spring- 

 in the hub opposite to the cylinder in question. 



The pulley (pul, pi. 24, fig. 5) is 77 mm. in diameter and 

 14 nun. thick with an asymmetrical groove 13 mm. deep. It 

 serves to carry the elastic string which binds the adjacent 

 margin of the net to the hub (el, pi. 24, fig. 5 ; pi. 23, fig. 4) . It 

 is obvious from a comparison of figures 1 to 4 (pis. 22 and 23) 

 that the margin of the net adjacent to the hinge, when the net 

 is closed, encircles nearly the whole of the pulley, except only 

 the part included in the width of the closed jaws, while in the 

 open net (pi. 23, fig. 4) it is compressed to less than one-half 

 of the circumference. The elastic tie-string (el.) passes around 

 in the groove of the pulley and through a fold in the margin of 

 the cloth head-piece of the net of a length sufficient to stretch 

 over the necessary part of the pulley when the net is closed. 

 This insures a plankton-tight junction of the net and its rim in 

 this critical part of the apparatus. 



The jaws proper are semicircular, flattening to rectilinear as 

 they approach the hub. They (pi. 25, figs. 12, 13) are 40 mm. 

 wide, 14 mm. thick at the base (&.), and 5 mm. on the square 

 lip (/.). For a distance of 30 mm. back from the lip the sur- 

 face of each is beveled (hev.) so that when the jaws are closed 

 the two beveled surfaces are in immediate contact to the 

 shoulders (sh.), thus insuring plankton-tight closure. 



The structure of the trips (tr.^ and tr.^, pi. 24, fig. 9 arid 

 pi. 25, fig. 15) is simple. There are two, the one nearer the 

 axis (tr.^) being operated by the first messenger and the outer 

 one (/;•.-) by the second. Each is located in a separate vertical 

 trip chamber (tr. ch.) in the head-piece of the frame and con- 

 sists of a shaft (shaft) about which is a coiled spring (c. sp.) 

 which draws the clutch (cl.^ or cl.-) on the lower end of the 

 shaft firmly up against the projecting hook of the rim of the 

 jaw of the net (hk.^ or hk.-, pi. 24. fig. 9). These lugs are hooked 

 and hold the jaws firmly in place. Each messenger strikes not 

 only the trip but a second pin (huf.^, huf.-) on the opposite 



