414 PROCEEDINGS OF THE AMERICAN ACADEMY. 



10. Llmax maximus, on account of the inconstancy of its photo- 

 tropic responses, was fourd to be unsuitable for these experiments. 



11. The results of the experiments upon the cricket frog (Acris 

 gryllus) will be found concisely enumerated on p. 400. 



12. The results of the experiments upon the green frog {Rana 

 clamata) are enumerated on p. 401. 



13. The animals which showed by their reactions the most evidence 

 of discrimination between the two lights (viz., Vanessa, Ranatra, and 

 the two species of frogs) are all positive in their ordinary phototropic 

 responses. 



14. The negative animals experimented upon (earthworm, land 

 planarian, mealworm, sow bug, cockroach) showed little or no ability 

 to discriminate between the two areas of illumination, but appeared to 

 respond almost entirely to the intensity of the lights. 



15. These reactions are correlated with the natural habits of the 

 animals. 



16. There are certain positive forms (especially larvae of Lepidop- 

 tera and certain marine Copepoda) which apparently respond to light 

 intensity only ; but these are prevented by the conditions under which 

 they live from being brought into unfavorable circumstances by their 

 movements toward the light. 



17. The responses of animals to light may be divided roughly into 

 the following types: 



Type A. Response of eyeless forms. Usually negative ; sometimes 

 positive, and then usually to very weak light. Respond to intensity of 

 light only (e. g., earthworm). 



Type B. Response of forms with ^^ direction eyes." Usually negative 

 (e. g., Bipalium, Periplaneta, Tenebrio larva) ; sometimes positive 

 (e. g., larva of wood-borer), in which case special adaptation prevents 

 their following the light until it brings them into unfavorable 

 conditions. Response almost wholly to intensity of light. 



Type C. Response to size of luminous field. Animals usually 

 positive, though they may be temporarily negative, as was seen to be 

 the case with the frog, for example. Probably the response to the size 

 of the field is adaptive only when they are positive. 



Type D. Response to definite objects in the visual field. Not simple 

 reactions ; responses usually involve psychic phenomena. Respond 

 (1) to moving objects, (2) to stationary objects. This form of response 

 usually inhibits ordinary phototropic reactions. 



Types C and I) are developed together. 



The types outlined above do not necessarily represent a genetic 

 series. 



