90 'Journal of Cojuparatwe Neurology and Psychology. 



3. One may bring about artificially with the nemerteans the inversion of the 

 tropisms in the presence of chromatic rays while preserving the negative sense of 

 their phototropism with reference to white light. 



a. Placing Lineus in a solution composed of from 25 to 80 cc. of distilled 

 water to 100 cc. of sea water, I obtained on the following day this inversion with 

 absolute certainty. Lineus while remaining negative with reference to white light 

 now directs itself toward the most refrangible rays of the spectrum, just as it had 

 previously directed itself away from them. 



The result of the inversion is that the phototropism, which remains negative, 

 is here absolutely separated from the chromotropism, of which the sense is changed. 

 Every chromatic ray has a specific action and at the same time the action of white 

 light is not a simple resultant of a mechanical fusion of the actions of all the possible 

 rays of the spectrum. 



I must remark further, that I have not as yet found, in spite of long continued 

 researches, a single means of transforming the negative phototropism of Lineus 

 into positive phototropism by agents either chemical, osmotic or thermic. Thus, 

 for example, the animal remains negative until its death in the presence of white 

 light whatever the concentration of the sea water. 



b. The inversion of the chromotropism of the nemerteans appears the second 

 day, continues in general two days and disappears the fourth, the animal becoming 

 again normally erythrotropic. This seems to me to prove that the nature of chro- 

 motropism is not an absolute function of such orsuch vital medium but a function 

 of the physiological state of the organism, a fact which agrees with the observa- 

 tions of LoEB concerning the changes in heliotropism at different periods of life. 



c. There is one fact which confirms further this point of view, namely, that 

 my Lineus after having lived for two or three weeks in my solutions and presenting 

 consequently their normal chromotropism (erythrotropism) change anew when one 

 transfers them into pure sea water and become purpurotropic (direct themselves 

 toward the violet). 



But this is not all. 



d. The inversion of the chromotropism is not produced immediately and it 

 also does not disappear all at once. There are stages when the animal still 

 erythrotropic (normal) ceases to distinguish green from yellow. There are others 

 when though indifferent to green and yellow it is already purpurotropic. These 

 stages of tropic blindness with reference to the middle parts of the spectrum last 

 several hours and thus one can easily observe them on the second and the fourth 

 day. There should exist still two stages in the passage from erythrotropism to 

 purpurotropism and inversely, during which the animal is completely indifferent 

 in the presence of colored rays, that is, is achromotropic — either because it is equally 

 influenced by all the chromatic rays or because it is entirely insensitive. This I 

 have not yet been able to observe, for these stages are of very short duration. 



In a second note the author points out the following bearings 

 of his discovery upon the problems of general biology and of the 

 psycho-physiology of vision. 



