Reactions of 1 sopods 463 



J. General Siinunary of Expert nietifs zvith Meehauieal 



Stiniu/at/on 



To all kinds of mechanical stimulation, whether pure tactile 

 stimulation or mechanical vibrations, Ca::-cidotea is decidedly 

 more responsive than Asellus. This becomes evident both from 

 examining the frequency of response and the vigor of response, 

 Caecidotea responding more often and more vigorously than 

 Asellus. The difl^'erence in vigor of response is particularly 

 noticeable toward the stimuli of lower intensity to which Asellus 

 responds only very slightly, if at all; but Cscidotea, as long as 

 the stimulus produces any response at all, continues to respond 

 vigorously. 



The flagella of the antennae of both species were surprisingly 

 unresponsive to pure tactile stimulation by contact with bristles 

 or localized currents of water, but they seemed to be extremely 

 sensitive to vibrations such as those procuced by the tuning fork 

 or by the concussion of a falling body. While the latter was not 

 actually demonstrated, it w^as strongly indicated by the different 

 behavior of the animals under the two sorts of stimulation — pure 

 tactile and mechanical vibrations. When the flagellum of the 

 antenna did respond to tactile stimulation the response was usu- 

 ally accompanied, especially in Asellus, by a trembling or jerking 

 motion and a withdrawal of the stimulated part or a stroking or 

 rubbing of the whole antenna with the gnathopod. Such a re- 

 sponse occurred very commonly to stimulation by concussion and 

 by the tuning fork. With the concussions the stimulus was only 

 momentary and the response was of short duration, but quite 

 like the response to the vibrations of the fork, except that it was 

 not carried so far. To the vibrations of the fork the response was 

 quite often only the above-mentioned movements of the antenna? 

 and gnathopods. If the stimulus was continued without break, 

 however, these movements were usually followed by the animals' 

 crawling. In short, the responses to stimulation of the animal 

 as a whole by mechanical vibrations are the same as the responses 

 to local stimulation of the flagella of the antennae by pure tactile 

 stimulations. In the latter case the stimulation was local, and 



