390 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in the middle of the opening a small wooden cone, up which the flies 

 could easily climb. Nevertheless many still persisted in crawling out 

 at the edge of the opening in spite of the obstructions, while those 

 that climbed the cone usually came to rest on its sides instead of 

 climbing up to its apex and flying thence as it was hoped they would 

 do. Obviously, too, those which climbed the sides of the cone were 

 often shaded from one or the other of the lights by the cone itself, and 

 this introduced another chance for error. Finally, an outer paper cone 

 was so arranged as to make it impossible for the flies to come out any- 

 where except through an opening at its apex, from which there led a 

 narrow Y-shaped paper, one arm extending toward the large light, 

 the other toward the small, with strings leading upward to the traps 

 on either side. But even with this apparatus the tendency of the 

 flies to continue crawling up the edge of the Y upon which they hap- 

 pened to emerge appeared to overcome in large part their reaction to 

 light. With a single light — the large one — only about twice as many 

 individuals went toward the light as in the opposite direction ; and 

 when both lights were used the readings were almost equal — 222 

 to 226. 



From these results it will be seen that, although the eyes of Dro- 

 sophila would, from their structure, appear to be as well adapted to 

 image-formation as those of either of the other adult insects em- 

 ployed, the experiments with the two luminous areas of diff"erent size 

 furnish no data whatever to aid in the determination of this point. 



9. Garden Snail of Europe {Helix pomatia Linn.). 



These snails, during the winter months when they have withdrawn 

 into their shells for hibernation, are imported into this country by 

 certain French restaurants in the larger cities, and may in this way 

 be readily obtained in the living condition. Under the influence of 

 warmth and moisture they emerge and live well, so that they may 

 be kept in the laboratory for a considerable period. A few preliminary 

 experiments tried with them seemed to indicate that they were for the 

 most part decidedly positive in their reaction to light, often turniug 

 to it at once at a sharp angle. This led to the hope that they might 

 be suitable for experimentation in regard to the eff"ect of the two lights. 

 The snails were allowed to crawl on the ground-glass plate in the same 

 manner as described for the earthworm and laud planarian. They are 

 easily handled by the shell and can be placed in any position desired. 

 As in the case of the other forms, they were first oriented in the 

 " normal " position in the shaded area between the screens and then 



