192 LESLIE B. AREY AND W. J. CROZIER 



sq. mm., agreeing with the minimal area for attachment as found 

 by Parker and in our own tests. The local character of the suc- 

 tion mechanism of the foot is further suggested by the minute 

 depressions, usually long and narrow and more or less communi- 

 cating with one another, which are to be found on the foot of a 

 non-creeping Chiton attached for some hours to a glass plate in 

 air. These local suctions are probably assisted by slime secre- 

 tion, which, although small in actual amount, enables a chiton to 

 remain rather firmly attached to a smooth surface (e.g., of a 

 glass plate) after the animal has been allowed to die in air or 

 after it has been killed by heat (44°C.) in water. They do re- 

 main so fixed, even when the girdle is not in contact with the 

 substjatum, and the slime may therefore be important during the 

 use of the foot in life, including early postlarval stages (Heath, 

 '99, p. 640; separate, p. 65). 



IV. MECHANICAL EXCITATION 



1. Tactile stimulation 



In testing the local sensitivity of Chiton to tactile excitation, 

 use was made of a blunt-pointed dissecting needle, a glass rod, 

 or a blunt pencil-lead. In some instances, also, minute air 

 bubbles (formed at the end of a pipette) and several other means 

 of stimulation were employed. The responses observed when 

 different regions of the dorsal and ventral surface of Chiton were 

 lightly touched with one or the other of these objects are de- 

 scribed in the following summary. Attention was given to the 

 possibility that the responses of Chiton might vary depending on 

 whether the animal was submerged in water when tested or was 

 out of water. There were discovered no differences in behavior 

 which require consideration at this point when the reactions of 

 chitons in these two situations were compared. For the study 

 of the responses obtainable from the ventral surface, we have 

 mostly employed animals in air, placed upon their dorsal sur- 

 face. The inability of chiton to right itself, coupled with the 

 relative insensitivity of the shell surface, allowed us to work in 

 this way without introducing serious complicating disturbances. 



