Hadley, Behavior of the American Lobster. 20J 



over-lying box. The rays that thus passed through the black- 

 lined shaft and entered the box were practically parallel and at 

 right angles to the plane of the bottom of the box. It is clear that, 

 when the water in the box was very shallow, the rays of light pass- 

 ing up the shaft and striking the larvae could have no directive 

 influence, and that, when they passed through the graded light 

 screens or through plates of colored glass, placed just beneath the 

 glass bottom of the box, they could be effective only through 

 difference in intensity. 



Besides these boxes, use was made of certain glass jars, known 

 as museum or brain jars, which were for the most part cylindrical 

 in shape and varied in diameter from 20 to 25 centimeters. For 

 certain experiments these were covered wholly or partially about 

 their circumference with black paper, and the light was made to 

 come from the top, bottom, or through a "window" in the side, 

 as the case might require. 



In addition to the apparatus mentioned above, several kinds of 

 glass tubes were employed. Some were ordinary 15 centimeter 

 laboratory test tubes, while others had a length of 40 centimeters 

 and a diameter of 4 centimeters. These tubes were made with 

 rounded ends so that there would be no obstruction to the light 

 striking the tubes even at a slight angle, and the lobsters were 

 introduced through an opening in the top. Another type of tube 

 employed was the Y-tube, constructed of glass tubing, 4 centi- 

 meters in diameter as shown in Fig. 5. These proved exceed- 

 ingly useful in testing the reactions of young lobsters, both to the 

 intensity and the directive influence of the light rays, since the 

 arms of the Y-tube could be readily covered with colored glass 

 plates or fitted with black or white backgrounds, thus producing 

 different conditions of light in each arm of the Y. 



In many of the experiments it was desirable to use graded light 

 screens. These were made by adding india ink to a solution of 

 gelatine and allowing this to harden in the form of a wedge. The 

 wedge-shaped screen permitted light to pass through in diminish- 

 ing amount, from the thin edge to the thick edge, which was quite 

 opaque. Graded light screens of red and blue were also made by 

 adding to the gelatine a solution of eosin or methylene blue. 

 It was by means of these, together with the colored glass plates 

 that differences in the intensity of light were secured. 



Since a particular response to light is often interpretable only 



