294 'Journal of Comparative Neurology and Psychology. 



sequent positive or negative reactions. Nor do we understand 

 why, when the larva is in one " physiological state, " a certain inten- 

 sity of light (striking equally the posterior lateral surface of the 

 two eyes) causes a positive reaction, while if the same larva is in 

 another "physiological state," the same light (striking with the 

 same intensity the same parts of the eye-surfaces) causes the oppo- 

 site reaction; or again, why when the larva is in the same "physio- 

 logical state," one intensity of light causes a positive reaction, 

 while light of slightly less intensity determines a negative reaction. 

 No more do we know why the illumination of the upper surface 

 of the eyes (Fig. 22, d) causes a forward rotation; or the illumina- 

 tion of the lower surfaces (b), a backward rotation; or the illumi- 

 nation of the anterior surface (c), a forward or a backward rota- 

 tion. These as yet unexplainable conditions of reaction may well 

 convince us that, however simple and mechanical some of these 

 reactions appear to be, many of them are extremely complex, 

 and indicate a very complex relation between the different regions 

 of the eyes and the nervous centers. Yet, as has been stated, to 

 such a degree as any of these reactions can be explained, those 

 which are concerned in the processes of body-orientation are more 

 easily interpretable on the "simple-reflex" hypothesis. In view 

 of this fact the writer would differ from the conclusion reached 

 by BoHN (loc. cit., p. 41): "Tous ces phenomenes (the reactions 

 of larvae of Homarus vulgaris) sont en relation avec des etats 

 physiologiques particuliers. Sous I'influence de I'eclairement, 

 I'etat physiologique des larves de homard ne tarde pas a changer, 

 et les tropismes aussi. " The present writer would limit the appli- 

 cation of this theory to those reactions of the larval lobsters w^hich 

 are concerned with progressive orientation, excluding body-orien- 

 tation. 



Regarding the relation of the type of reaction found in the larval 

 lobsters to the tropism theories, inference has already been 

 made in the preceding paragraphs. First, to w^hat extent does 

 the behavior found in the larval lobsters agree wnth the local 

 action theory of tropism ^ The primary demand of this theory 

 is that the body of the organism should become so oriented with 

 respect to the source of illumination that the anterior end is made 

 to point either toward or from the source. Under these condi- 

 tions the index of reaction is said to be positive or negative, accord- 

 ing as the organism moves toward or from the light. "This 



