206 LESLIE B. AREY AND W. J. CROZIER 



especially upon the base of the foot, such as we suggest in the case 

 of geotropism. 



The effects of local currents were also tested. A current 

 from a pipette directed under the girdle of a submerged chiton 

 induces a depression of the girdle, provided the gills are disturbed. 

 A current directed upoh the girdle causes it to be depressed; it 

 can usually be seen, in this case, that the 'scales' upon the 

 girdle are moved or that the girdle itself is mechanically bent. 

 A current impinging upon the dorsal mantle between the shell 

 plates produces usually no effect. The girdle is the most 

 sensitive region. 



Negative reactions of the whole animal are readily induced by 

 repeated applications of a pipette current to a part of the girdle. 

 These reactions are also concerned, probably, in the orientation 

 of Chiton in a vigorous stream of sea-water. 



5. Geotropism 



Since the Amphineura lack the statocyst organs characteris- 

 tically developed in other molluscan classes, the question of 

 Chiton's behavor with respect to the pull of gravity deserves 

 special consideration. The positions in which they are commonly 

 to be observed strongly suggest that they are negatively geo- 

 tropic. The younger individuals, particularly, are found most 

 abundantly at the upper limit of the tidal reach. Older animals 

 occur over the whole intertidal zone, and even in some cases 

 slightly below it, but these, too, are most frequently encoun- 

 tered near the upper tidal limit. Furthermore it is very notice- 

 able, more particularly among the larger individuals, that the 

 great majority of the chitons taken from perpendicular rock 

 faces are oriented with the anterior end upward, rarely indeed 

 with this end directed downward, although in many cases they 

 are more or less nearly horizontal. When kept in aquaria they 

 rapidly creep to the water surface and sometimes thence out 

 into the air; nevertheless, they sometimes curl over the top of an 

 aquarium and creep downward on its outer wall (more espe- 

 cially in the case of aquaria with a free general overflow at the 



