282 W. J. Ceozier, 



also that reactions follow the direct application of dissolved electro- 

 lytes and food juices ("taste"). Both types of chemo-reception play 

 a part in feeding (Jennings 1907, Cowles 1910). The tube feet 

 are the most sensitive organs (Peouho 1890, Hamann 1883, Cuénot 

 1891, Cowles 1910). The oral tentacles of ophiuroids were believed 

 by Peeyer (1886) and Nagel (1894) to be sensitive also (cf. like- 

 wise V. ÜEXKÜLL, 1905). Synaptids have been thought to have 

 some chemical sense associated with the so-called olfactory cups on 

 the tentacles (Claek 1901a). 



Peaese (1908, p. 275) found TJiyone to react negatively to 

 supposed food extracts; this, together with Nagpl's brief statement 

 on Cucumaria: — „Diese überaus trägen Tiere zeigen jedoch voll- 

 kommene Gleichgiltigkeit gegen alle von mir angewandten süßen und 

 bitteren Eeizstoffe" (Nagel, 1894, p. 178) —, and a few experiments 

 of Polaea (1906) are the only observations known to me on the 

 reactions of holothurians to chemical stimuli. 



The normal feeding of H. surinamensis probably is not especially 

 concerned with chemical sensitivity; it is more likely merely a 

 complex of tactile responses, as seems to be the case with many 

 synaptids. The reactions obtained to dissolved substances were of 

 a strictly negative kind, and I have therefore not dealt with this 

 phase of the problem. 



Experiments were made with the object of demonstrating the 

 range of substances to which Hoïothuria is sensitive, the distribu- 

 tion of this sensitivity over the body, and such quantitative aspects 

 of the reactions as would permit of comparison with the physiology 

 of chemo-reception in other animals. 



2. Method; reactions obtained. 



Qualitative experiments in which the stimulus was applied to 

 various parts of the animals in the form of solutions, or, in the 

 case of the essential oils, used directly, showed that all portions of 

 the surface of Hoïothuria were sensitive to salts, acids, alkalies, 

 alkaloids, certain carbohydrates, various other organic substances, 

 and essential oils. All the reactions, with one exception, were of 

 the negative kind previously described under the reactions to 

 mechanical and photic stimuli, tending toward the removal of the 

 part affected from the field of stimulation. The one exception was 

 in the case of magnesium chloride in M/10 solution; the tube feet 

 did not react negatively, but in most cases extended and frequently 



