284 W. J. Ceozier, 



3. Quantitative experiments. 



For tests designed to be on a more exact basis, the following 

 method was employed: 



Solutions of the materials to be used as stimulants were made 

 up on a gram-molecular basis at 25", usually M/10, with filtered 

 rain water. The stimulus was applied by allowing 0,5 cc to flow 

 gently over the desired region from a pipette the tip of which was 

 held one-half centimeter away from the point to be stimulated. The 

 reaction time was measured (with a stop watch reading to 0,1 sec.) from 

 the time of application of the stimulus until some movement was 

 given by* the animal. The tests were made in diffuse light, to avoid 

 shadow stimuli. The rain water used w^as tasteless, neutral to in- 

 dicators, and in sunlight algae grew in it (so it was not toxic in 

 this sense); analysis showed the presence of minute amounts of 

 calcium chlorides and sulphates, such impurities being expected, as 

 the water was collected from whitewashed lain sheds. For the pur- 

 pose of the present experiments, it was essentially "distilled water". 

 The chemicals employed were all Merck's materials of high purity. 

 Many careful tests showed that under the conditions of these ex- 

 periments rain water in itself did not constitute a stimulus. Holo- 

 thuria did not react to solutions of merely high or low osmotic 

 pressure — a condition which is, I believe, correlated with the fact 

 that, living as they do near low-tide level, these animals must fre- 

 quently be exposed to dilution of the sea water by heavy down- 

 pours of tropical rain. Henei et Lalou (1903) found the exposed 

 membranes of HolotJmria and Stichopus to be efficient semipermeable 

 membranes, permitting the osmotic regulation of the internal fluids 

 in a fairly rapid manner. In my experiments rapid death, however, 

 resulted from sudden immersion in rain w^ater, as shown by the 

 following : 



Expt. 82. 

 July 20. Temp. 25, 1». 

 A.M. Elapsed 



10.30 time Four holothurians plunged into 1 liter of rain 

 (minutes) water. 



10.31 1 Tentacles and podia retracted. Green pigment 



becoming dissolved out. 

 10,55 25 One animal dead ; another has begun to eviscerate. 



Further pigment loss. 



