1 88 HOLMES. [VOL. II. 



Raising the temperature has the effect of making Gammarns 

 mncronatus positively phototactic, but an increase of only a few 

 degrees beyond the point where its phototaxis changes pro- 

 duces heat rigor. Possibly Amphithoe might be rendered 

 positively phototactic could it endure a somewhat higher 

 temperature. 



Neither increasing nor decreasing the concentration of the 

 sea water was found to effect a change in the direction of 

 phototaxis. A more extended account of phototaxis in the 

 Amphipoda will appear in another paper. 



TJiigmotaxis. 



The tendency of Amphithoe to keep in contact with solid 

 objects is one of the most conspicuous features of its behavior. 

 This tendency is apparently one of the fundamental instincts 

 of the group, as it is exhibited very strongly by most of the 

 Amphipoda. When placed among branched seaweeds, Amphi- 

 thoe stops only after it works its way among the branches 

 where there is contact on several sides of the body. In Ulva 

 it comes to rest in a fold of the frond. When placed in a glass 

 dish containing nothing but sea water, it swims about restlessly 

 and eventually comes to lie quiet in the angle between the 

 bottom and side. The instinct to crawl into an empty nest 

 is an expression of the same tendency. Were it not for its 

 thigmotaxis, the whole conduct of the animal would be very 

 different from what it is. Many other instincts, like the nest- 

 building instinct and the instincts associated with it, are built 

 upon this fundamental reaction as a foundation. It does not 

 seem improbable that the instinct of the female to remain 

 perfectly quiet while carried about by the male, and even the 

 strong propensity of the male to seize and retain hold of the 

 female, may be but modified and specialized forms of thigmo- 

 taxis. Given variations of responsiveness to contact in differ- 

 ent parts of the body, and variations in the manner in which 

 the responsiveness is exhibited, we would have the means by 

 which thigmotaxis might be modified by natural selection into 

 more specialized forms of behavior. If the origin of the various 



