KEPORT OF COMMISSIONERS OF INLAND FISHERIES. 215 



We have learned, furthermore, that these same fourth-stage larvae 

 of all ages, under experimental conditions, will usually shun the light 

 when it has a single directive influence, and travel in the direction of 

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

 the fourth-stage larvae, except those in the latter part of the stage 

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

 water, where they swim actively during a large part of the fourth 

 stage-period. The question now arises: What is the cause of this 

 surface swimming of the fourth-stage lobsters, under normal condi- 

 tions? Is it a response to intensity of light, to the directive influence 

 of light, to hunger, or is it perhaps a form of geotaxis? Although 

 we know something of the individual workings of several of these 

 reaction factors, we need to be cautious in deciding upon their indi- 

 vidual instrumentalities when they have opportunity to work in 

 combination. If we can discover, however, 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, so is the other, — then, and then only, are we justified 

 in believing that we know the determining cause of the particular 

 type of natural behavior in question. We have such a parallel 

 between the j^hotopathic reactions and the surface-swimming ten- 

 dency 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 such a 

 parallel before us, it can not 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. 

 This view is further supported by the fact that the early fourth- 

 stage larvae could, at night, be drawn into a region illuminated by 

 means of acetylene lanterns. Late fourth-stage larvae would never 

 manifest this reaction so clearly, and often appeared even to be 

 repelled by the influence of the light. 



