(362 



RAYMOND PEARL. 



the solution introduced, the rate of its diffusion through x 

 into the water could be very nicely controlled. This matter 

 was thoroughly tested, and the apparatus in a sense 

 calibrated by the use of coloured solutions before the actual 

 experiments were begun. 



A considerable number of experiments were tried with this 

 diffusion trough, with the following results : — In no case was 

 there any observable orientation of the organisms. A typical 

 experiment will illustrate what actually took place. A 

 ■g^ per cent, solution of NaX'Og,, Avhich by the capillary 

 method always produces a sharp positive reaction, was put 



Pig. oS. — I. Diffusion trough used for testing the reactions of planarians 

 to diffusing clieuiicals. A, A. Ghiss base i)hite. U, 1>, 1>. raiafliu 

 tioui;ii. .r. Point of opening of diffusion tube. C. Cavity of 

 trough in whicli the s])ecimens are placed. D. Tube in wliicii the 

 solution to be tested is placed. II. Enlarged sectional view of the 

 end of the trough bearing the diffusion tube. Lettering as in I, 



into the tube D in sufficient quantity to give a diffusion of 

 moderate rate. After it had been diffusing for some time (by 

 test with coloured solutions long enough to reach the middle 

 of the trough) specimens were introduced at the end C. 1'hey 

 started gliding about in random directions at once. Some 

 passed diagonally up to the end D ; others remained nearer 

 the end C ; while still others went up on the paraffin sides to 

 the end D. None went straight towards ,(• after they had 

 come into the region where the chemical liad diffused. No 

 reaction of any sort was given in the course of the passage 



