426 H. p. KJERSCHOW AGERSBORG 



tentacles, the anterior quarter being white. In normal specimens 

 they are in constant motion, being generally directed from the 

 head at an angle to each other of about G5°. When the animal 

 moves, they are directed forward and sidew^ays in a lashing fash- 

 ion, the tips being the most motile parts. 



The dorsal tentacles are situated on the top of the neck, one 

 on each side of the red median dorsal line, and 1.5 to 2 mm. 

 back of the anterior border of the foot. They are about one-half 

 the length of the oral tentacles and they are directed almost 

 vertically from the body, or sometimes at an angle to each other 

 from 0° to ca. 23°. In external structure, they differ from the 

 oral tentacles, which are smooth, in that they are .supplied with 

 a series of prominent annulations. Like the former, they are 

 white at the ends. For experimental purposes, I selected at 

 random a number of large and small individuals, which I paired 

 into a number of sets, each consisting of a small and a large 

 individual (vide ut tabula). 



Tactile stimulation. The entire surface, including the papillae, 

 the parts between the papillae, the foot including the lanceolate 

 posterior prolongation which extends back of the papillae com- 

 monly up to one-half the length of the body, the oral and dorsal 

 tentacles, and the anterolateral prolongations of the foot, is 

 sensitive to touch. The tentacles are more sensitive to touch or 

 tactile stimuli than are any other parts of the body. It is hard 

 to tell which of the tentacles are the most sensitive to tactile 

 stimulation, because the oral tentacles are frequently in constant 

 motion, but judging from the response obtained when the two are 

 touched similarly, it appears that the dorsal tentacles are the more 

 sensitive of the two, at least to tactile stimuli. That is, an 

 equally gentle touch to them gives a more effective response in 

 the dorsal tentacles, in that they not only contract by shortening 

 relatively more, but also by remaining retracted longer than the 

 oral tentacles. The oral tentacles may shorten a little, but their 

 main response to tactile stimulation consists in being jerked 

 away from the stimulus and then be put back at once to their 

 former or similar position. 



