Hadley, Behavior of the American Lobster. 291 



of groups of lobster larvae can in no way be readily predicted. One 

 exception to this may be stated. The first-stage larvae, directly 

 after hatching, would be strongly drawn to the surface of the 

 water by virtue of both their photopathic and of their phototactic 

 response. After the first day or two, however, begins that modi- 

 fication and variation in the phototactic action which, for groups 

 of uncertain age and condition, makes any accurate prediction of 

 their movements quite impossible. 



In the case of the fourth-stage lobsters there is a better basis 

 for the correlation of the natural and experimental types of behav- 

 ior. We know that, under experimental conditions, hungry 

 fourth-stage larvae, when submitted to food stimuli, will rise imme- 

 diately to the surface of the water and swim about excitedly for 

 some moments; we know also that the early fourth-stage larvae, 

 under certain experimental conditions will leave a region of low 

 light intensity and remain in regions of greater light intensity. 

 We have learned, moreover, that the same fourth-stage larvae, 

 under different experimental conditions, will usually shun the 

 light when it has a single directive influence, and travel in the direc- 

 tion of the rays away from their source. Finally, we have observed 

 that the fourth-stage lobsters, except in the latter part of the stage- 

 period, show a definite tendency to remain at the surface of the 

 water. 



The question now arises: What is the cause of this surface- 

 swimming ^ Is it a response to the intensity of light, to the direc- 

 tive influence of light, to hunger, or to gravity ^ Although we 

 know something of the eff'ects of several of these factors when they 

 act separately, it is difficult to ascertain their individual influence 

 when they work in combination. If, however, we can discover 

 any parallel between a certain type of reaction under experimental 

 conditions and a certain mode of behavior under natural conditions, 

 and find that as one is modified or lost the other is also, then, 

 and then only, are we justified in believing that we know the deter- 

 mining cause of the particular type of natural behavior in question. 

 We have such a parallel between the photopathic (and occasionally 

 the phototactic) reactions and the surface-swimming tendency of 

 the fourth-stage lobsters. As the former becomes modified and 

 is eventually replaced by the negative reaction, so the latter is 

 changed and finally gives way to the bottom-seeking tendency 

 as the lobsters pass on through the fourth stage-period. With 



