350 PROCEEDINGS OF THE AMERICAN ACADEMY. 



opa Linn.). 7. The water scorpion {Banatra fusca Pal. B.). 8. The 

 pomace fly {Drosophila ampelophila Loew). 9. The common garden 

 snail of Europe {Helix pomatla Linn.). 10. The cricket frog {Acris 

 gryllus Le Conte), and the green frog [Tiana clamata Daudin). 



Below are set forth the results of the experiments on these animals 

 in the order given above. The statement of results is followed by a 

 discussion of their significance. 



1. Earthworm {Allolobophora foetida\^d,Y.'[). 



In connection with observations upon the reactions of a series of 

 animals having eyes of different kinds and of varying degrees of com- 

 plexity, it seemed desirable, for the sake of comparison, to make similar 

 observations upon a form without eyes. Of all the forms available, the 

 earthworm appeared to be the best suited to this purpose. A number 

 of observers have worked with earthworms of various genera, so that 

 their behavior in relation to light is better known than that of many 

 other animals. Although there appear to be differences in the degree 

 of sensitiveness of different species, the behavior of the several kinds 

 that have been studied seems to be essentially the same. 



That earthworms ordinarily respond negatively to light of moderate 

 intensities was early remarked by Hoffmeister ('45), and subsequently 

 by Darwin ('81), and has been abundantly confirmed by all later 

 workers. For the purpose of the present investigation it was sufficient 

 that the worms react in this manner in a large percentage of cases, 

 and that they lack eyes, — that is, any organs for focussing the light 

 upon special sense cells. The fact that they possess such special cells 

 as the so-called light cells, — demonstrated by Hesse (96) and shown 

 for Perichaeta by Harper (:05), — has no bearing in this connection, 

 since there is no contrivance for concentrating the light upon these 

 structures. Nor does it matter that the animal is sensitive upon all 

 parts of its body, though to a different degree in the different regions, as 

 shown by Parker and Arkin (:01). Indeed, it is unimportant to know 

 in what manner the reaction is brought about ; whether it is a direct 

 response, in the sense of the tropism theory, or a result of trial and 

 error, as maintained by Holmes (:05) and confirmed for moderate in- 

 tensities of Hght by Harper (:05), since the problem is merely to deter- 

 mine, as indicated by the direction in which the animal moves, whether 

 it is more strongly stimulated -upon one side than u})on the other. 



Method of E.rper'niwntation. The luminous areas, as previously ex- 

 plained, were fixed, one at the left and one at the right of the experi- 

 mentation table. Earthworms in good condition, which had previously 



