292 journal of Comparative Neurology and Psychology. 



such a parallel before us, it cannot be doubted that there exists 

 a certain causal relation between the positive photopathic reaction 

 and the surface-swimming tendency on the one hand, and the 

 negative photopathic reaction and the bottom-seeking tendency on 

 the other. But the photopathic reaction may not alone be respon- 

 sible for the surface-swimming tendency on the part of the fourth- 

 stage lobsters. The presence of food particles in the water excites 

 them strongly, and causes them, when in the glass jars, to swim 

 excitedly at the surface of the water. It therefore appears quite 

 within the bounds of possibility that chemotropism may also play 

 a part in determining the surface-swimming of the fourth-stage 

 lobsters. 



The explanation of the behavior of the fifth and all later stages, 

 in the light of the foregoing experiments, rests upon a more certain 

 basis. We have observed that the fifth-stage lobsters invariably 

 manifest both a negative phototactic and a negative photopathic 

 reaction. In general this may be said to explain the fact that 

 lobsters in the fifth and all later stages shun the light at all times. 

 Little work was done on the behavior of the older lobsters, and it 

 is hoped that future investigations may continue along this hne. 



In connection with the mechanics of orientation, the writer has 

 shown that the reaction of larval lobsters to light is made up of two 

 components — body-orientation and progressive orientation; and 

 that the former is primary while the latter is secondary. In the 

 earlier pages of this paper it was demonstrated that the progressive 

 orientation is dependent upon a great number of conditions, and 

 that the orientation responses are relatively complex reactions 

 which are dependent in great measure upon the obscure, changing, 

 internal conditions which are embraced under the general term, 

 "physiological states." In later pages, on the other hand, atten- 

 tion has been directed to those conditions of light which deter- 

 mine the body-orientation alone; and the results recorded have 

 made it clear that the movements producing the body-orienta- 

 tions are types of action which simulate more closely pure reflexes, 

 direct, constant, and invariable. 



As BoHN (1905a) has well said, it is impossible to take definite 

 account of the complicated series of phenomena which take place 

 in the nervous system of animals even as low as the arthropods, for 

 these are dependent not alone upon complicated connections 

 between neurons, but also upon their variable states. Yet it is 



