248 'Journal of Comparative Neurology ajtd Psychology 



the case in earlier stages, by using different intensities of light 

 (3) The photopathic reaction, which in the early fourth-stage 

 lobsters is definitely positive, changes by the latter part of the stage 

 to negative in the majority of individuals. Thus it can be observed 

 that, just as the third-stage larvae might at the same time (or suc- 

 cessively) manifest both a negative phototactic and a positive pho- 

 topathic reaction, so may the lobsters of the fourth stage. Other 

 points regarding the behavior of fourth-stage lobsters will receive 

 consideration in connection with the subject of contact-irritability. 



5. Fifth Stage. 



The body-form of the fifth-stage lobster is similar to that in the 

 fourth-stage, and we might therefore expect to find similar types 

 of reaction. It will be seen, however, that there are . many 

 points of difference in behavior which are of such a nature that 

 they can not be attributed, either wholly or in part, to changes in 

 body-form or in the swimming appendages. The changes are 

 doubtless the consequence of modifications which have taken place 

 in the body-processes or in the physiological states of the lobsters 

 themselves, and which have resulted from the cumulative stimula- 

 tion during the earlier life of the lobsters. Generally speaking, 

 it may be said that the reactions of the fifth-stage lobsters are fairly 

 typical for the adult form, and are especially characterized by 

 the light-shunning tendency. This form of behavior could be 

 observed readily by watching the lobsters in their confinement 

 cars; but, for the sake of certainty, the same experiments, to which 

 the larvae of earlier stages had been subjected, were repeated with 

 the fifth-stage lobsters. Since the reactions did not appear to 

 undergo any noticeable modification as the lobsters passed through 

 the fifth stage, there is no need for considering the early, mid and 

 late fifth stage-periods separately, as was done for fourth-stage 

 lobsters. The type of reaction presented in the early fifth stage- 

 period differs in no way from the behavior of lobsters in the late 

 fifth stage-period; and both are characteristic of the behavior in 

 all later stages. 



Experimerjt 2J. Case I. Photopathic reaction — In the first 

 instance, ten fifth-stage lobsters were transferred from one of the 

 confinement bags to the glass-bottomed box and this was placed 

 over the light-shaft. The method used was the same as in pre- 



