204 LESLIE B. AREY AND W. J. CROZIER 



When placed upon a glass plate the animal quickly puts its 

 whole foot in contact with it. In doing this, waves are set up 

 frequently and three or four may appear upon its surface at one 

 time; or, if the foot is already in nearly one plane, the attach- 

 ment may be almost simultaneous over its whole extent. In the 

 latter case, the local areas of the sole which are not at first 

 attached are brought down to the substratum. 



As noted by Olmsted ('17 a), a chiton repeatedly forced to 

 creep backward, by requiring one-fourth of the foot to attach 

 to the lower edge of a glass plate held vertically in air, becomes 

 after several trials exhausted, so that it creeps just sufficiently 

 to enable the whole foot to be in contact with the plate. 



Thus, to contact with a small area, such as a needle point or 

 the rounded point of a pencil, the resting foot of Chiton reacts 

 negatively, but to larger surfaces the response is a positive one. 

 There is a very pronounced tendency to keep the whole of the 

 foot in contact with some foreign surface. In no case has a chiton 

 ever been seen in nature with any section of the foot or head 

 completely removed from the substratum. This response is 

 sufficient explanation of the behavior of Chiton in 'righting' 

 itself. At no age is there a detectable tendency for chitons to 

 preserve an upward orientation of their dorsal aspect, even when 

 placed so that it is physically possible for the animal to reattach 

 itself {vide siipra, p. 200) ; undirected movements finally result 

 in a portion of the foot, usually the anterior end, effecting con- 

 tact with the substratum; complete reattachment is then rapidly 

 brought about. 



It is of interest to inquire if this form of tactile discrimination, 

 favoring attachment to a sufficiently large area of surface, is 

 evidenced by parts other than the foot. The ventral surface of 

 the girdle and the head region were therefore examined. 



Finer degrees of tactile discrimination seem to be absent on 

 the head and foot. Chiton shows no preference, when placed in 

 an aquarium, for surfaces such as those to which it has been 

 accustomed. Provided the surface be firm and sufficiently large, 

 it creeps indiscriminately over smooth stones sparsely sprinkled 

 with sand, glass, or wet paper. It will not creep, however. 



