84 CHAS. \V. HARGITT. 



cordingly the special aquaria were made use of, and the following 

 account is based entirely upon the behavior under tin- new con- 

 ditions. Two were used for the definite purpose of making of 

 one a control of the other. That is, given identical conditions 

 of temperature, food, etc., will the mere difference of direction 

 or intensity of light show itself in such measure as to warrant 

 conclusions? 



This series was begun on January 15 with twelve specimens, 

 eight being placed in the experimental tank, and four in the 

 control tank. The bottoms of the aquaria were covered by a 

 layer of rather coarse, black sand to facilitate attachment, and 

 at the same time to render any access of light from the bottom 

 impossible. The test tank was covered on three sides and the 

 top with an opaque hood, painted black on the inside and so 

 adjusted as to render inspection easy without disturbing the 

 specimens. In this tank the eight specimens were placed with 

 heads facing away from the source of light. Similar disposition 

 was made of the four specimens of the control tank. In about 

 three days the specimens had apparently attached themselves, 

 and on January 19, four days after beginning, one specimen began 

 an upward curve. On the 2ist several had shown such reaction 

 and by the 25th several had curved upward to from 25 to 50 

 degrees. In the control tank similar responses began to appear. 



On January 25, ten days after beginning, the record is as 

 follows: Of the eight specimens two have curved toward the light, 

 two are nearly vertical, two face toward the side, while two remain 

 as planted. Essentially the same condition obtains in the control 

 tank. One faces the window, one nearly vertical, and two as 

 originally located. 



At the end of four weeks, February i i, three show apparent 

 light reaction, two are nearly vertical, two remain facing away 

 from light, and one shows an indifferent curve laterally. The 

 positions in the control tank remain as before. Repeating Loeb's 

 experiment at this point, I no\v rotated the aquaria through 180 

 degrees, so that everything was changed directly about. Con- 

 ditions went on as before, the test tank receiving light exclusively 

 from one end, the control receiving diffuse light from the room 

 as well as the direct light from tin- window. On February 25, 



