10 Illinois State Laboratory of Natural History. 



brace-, main-, and end-stakes, respectively three, four and one 

 half, and five meters in length, complete the apparatus nec- 

 essary for making an oblique haul. 



4. Operation of the Oblique Hani (Plate III.). — In this 

 operation two persons are required, an oarsman to handle the 

 skiff and an operator for the apparatus. The method of pro- 

 cedure is as follows. The brace rope (Fig. 7, b. r.) is fastened 

 near the lower end of the brace stake {b. s.) and the latter is then 

 set as firmly as desired. The main stake (;//. s.) is then put in 

 place and the brace rope is tied to it. Next, the carriage rope 

 (e. r.) is fastened to the main stake {m. 5.) at a point 5 to 8 meters 

 distant from the thirty-meter knot {m). The boat is then 

 rowed away in line with the two stakes and the carriage rope 

 is unreeled until the end is reached, when it is run through the 

 pulleys (Fig. 6,/. and p.') of the upper part of the carriage. 

 The end knot {k.) is then tied and fastened to the rear pulley 

 (/.') by the release thread (///.). The carriage rope is next 

 tied to the lower part of the end stake (Fig. 7, e. s.), and at a 

 point just in front of the anterior pulley {p.) it is bound to 

 the end stake l)y the release line (r. /.). The lower part of 

 the carriage with the suspended plankton net can now be 

 attached to the upper j)art, and the end stake is ready to be 

 placed. When the end stake is set, the carriage line (Fig. 

 7, e. r.) runs obliquely from the release line to the surface of 

 the water at the main stake. The net occupies the position n. 

 (Fig. 7), and having l)een lowered vertically does not strain 

 any water in its descent. After placing the end stake the 

 skiff is rowed to the main stake as the draw-line (Fig. 1 ,d.l.) of 

 the carriage is unreeled. A quick jerk upon the carriage rope 

 snaps the release line (/-. /.) on the end stake, and the slack 

 in the carriage rope can l)e taken up at the main stake. Tha 

 carriage rope and net now take the position e. r.' and n.' 

 (Fig. 7), and the thirty-meter knot jn is at the surface of the 

 water. Everything is now in readiness for making the catch. 

 At the signal the release thread {th.) which binds the rear 

 pulley to the end knot is broken by a quick pull upon the 

 draw-line. The carriage l)earing the plankton net is drawn 

 up the oblique rope the distance of thirty meters in one minute 



