328 University of California Puhlications in Zoology. [Vol.8 



deep, for insertion of the key used in setting the coiled spring. 

 The side of the cylindrical head is bored with twelve equidistant 

 holes, 7 mm. in diameter, for the set screw (pi. 23, fig. 4; s. scr., 

 pi. 25, fig. 6) which holds the axis (ax.) in place when the spring 

 is set. Wound around the shaft is a coiled spring (r. coil sp. and 

 I. coil sp.) of heavy steel Avire which makes about twelve turns 

 around the shaft and has its inner and outer ends fixed respec- 

 tively in the end of the jaw and in the head of the axis. Sur- 

 rounding the shaft is a narrow chamber (sj). ch.), 8 mm. wide, 

 in which the coiled spring, whose wire is 4 mm. in diameter, has 

 some room in which to come and go, as the tension is changed. 

 The outer wall of this chamber is formed by the inner cylinder 

 (in. cyl.). Between the head (hd.) of the axis and this chamber 

 for the spring and resting against the outer ends of the inner and 

 outer cylinders, is a circular washer (w.) 82mm. in diameter, 

 2 mm. thick, with central orifice 25 mm. in diameter. 



The inner cylinder is 60 mm. in outside diameter, 82 mm. in 

 length, has a wall 10 mm. thick, and central opening 39 mm. in 

 diameter. The cylinder is continuous on the right side (of the 

 figure) with the lower jaw and on the left side with the upper, 

 that is, each inner cylinder is a part of a different jaw. From 

 this method of construction it follows that the lower jaw is 

 actuated by the spring of the right side (of figure) and the 

 upper one by that of the left. 



The outer cylinder (out. cyl.) is 82mm. long and 82 mm. in 

 diameter, with wall 10 mm. thick, and central opening 60 mm. in 

 diameter. This cylinder is structurally continuous upon the 

 right side (of figure) with the upper jaw, and on the left with 

 the lower. The relations of the inner {in. cyl.) and outer {out. 

 cyl.) cylinders respectively to the lower (/. j.) and upper {up. j.) 

 jaws respectively are clearly shown in the views looking from 

 the center of the opening of the net toward the hub, with the 

 pulleys (puL, pi. 24, figs. 7, 8) removed. With this method of 

 construction it will be seen that the outer cylinder is perfectly 

 free to turn around the inner cylinder between the outer washer 

 {w.) which is held by the outer terminal of the coiled spring to 

 the head (JhI.) of the axis {ax.), and the inner pulley {pul.) 



