216 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



But the photopathic reaction may not alone be responsible for the 

 surface-swimming tendency on the part of the fourth-stage larvse. 

 As has been shown, the presence of food particles in the water excites 

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

 excitedly at the surface of the water. This tendency was never 

 manifested by the fifth-stage lobsters. It therefore appears quite 

 within the bounds of possibility that hunger and the stimulation by 

 food particles in the water may also play a certain part in determining 

 the surface-swimming characteristic of the fourth larval stage. 



There is little advantage to be gained by attempting to explain 

 the natural behavior of the lobster larvse of early stages, on a basis 

 of the tropisms. It is true that they usually do select the regions 

 of greater light intensity. On the other hand, the directive influence 

 of the light rays may determine at one time a positive reaction, at 

 another, a negative; and these reactions may follow each other in 

 such rapid succession (depending on the intensity of the light and 

 the age or stage of the larvae) that the general reactions of groups 

 of lobster larvae, or of isolated individuals in question, could 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 not only their positive 

 phototactic, but also their positive photopathic reaction. After the 

 first day or two, however, begins that modification and variation in 

 the reactions which, for groups of uncertain age, makes an accurate 

 prediction of their movements impossible. 



The explanation of the behavior of lobsters in the fifth and in all 

 later stages, on a basis of the tropisms, is a far different matter. We 

 have observed that the fifth-stage lobsters invariably manifest both 

 a negative phototactic and a negative photopathic reaction. This 

 circumstance explains well enough the fact that lobsters of the fifth 

 and all later stages shun the light at all times.* 



*The objecfof the present paper has been to present briefly the results of an investigation, 

 the complete details of which will be published at a later date. 



