444 'Journal of Comparative Neurology and Psychology. 



a single pounce without any preliminary movement to get in 

 position. It might seem from this that the nicely coordinated 

 movement employed in seizmg food is not in response to the visual 

 impulse alone, but that the stimulation of the sensory bristles at 

 the same time serves to intensify the visual impulse. The negative 

 response may be called forth by stimulating with a fine glass rod 

 tipped with sealing wax. When so stimulated on either side the 

 animal makes a movement away from the stimulating object. 

 It may thus be guided across a vessel in a zigzag path by alter- 

 nately stimulating the opposite sides. 



When the stimulus causing the negative response is repeated 

 by a rapid succession of taps and intensified, the larvae appear 

 to become highly alarmed and project themselves with great force 

 and rapidity in long zigzag paths by a rapid succession of move- 

 ments. It is obvious that the intensified negative response is 

 of no small importance and that the security of these animals 

 does not lie wholly in their transparency. 



Acclimatization to such stimuli as tapping on the aquarium 

 jar is soon produced by repetition of the stimulus at closer inter- 

 vals. The responses become weaker until only a slight ducking 

 of the head is produced and finally no further response is made. 

 The dish in which the larva was placed was subjected to constant 

 tapping at one point and the movements recorded on a sheet of 

 paper by noting the position taken each time. The chart was 

 then reduced to the form shown in the figure. It will be seen that 

 the first eight or ten movements were all pointing in a general 

 direction away from the source of the stimulus. A chart of the 

 next movements shows them rather evenly distributed in all 

 directions (Figs. 2-3). 



REACTION TO LIGHT. 



In connection with the light responses of these creatures their 

 daily depth migrations furnish the matter of greatest interest. 

 It was noticed that Corethra's horizontal movements are restricted 

 on account of its lying-in-wait habit. If one may speak of the 

 orbit or range of an animal, it is of course a general fact that the 

 orbits of animals are most extended horizontally. In the case of 

 Corethra, however, the horizontal range is restricted, and the verti- 

 cal range is important and is largely regulated by gravity. The 



