THE SENSORY RESPONSES OF CHITON 175 



when the girdle is not detectably lifted ; this can be demonstrated 

 with suspended carmine. The girdle can, however, be very 

 tightly applied to a smooth surface. A chiton, if attached to 

 the wall of the dish, will live for two or three days completely 

 submerged in an aquarium containing other dead and decaying 

 chitons. During this time no water is taken into the gill chan- 

 nels. Hence, although chitons appear to frequent regions where, 

 by wave action, the water is well aerated, it does not appear 

 that they are particularly sensitive to want of oxygen.^ 



6. Migrations; association in groups 



The larger chitons rarely engage in creeping movements 

 unless they are at least partly under water. Occasionally they 

 are seen to creep about when the wet under surfaces of rocks on 

 which they may be situated are turned over and exposed to the 

 light. They also creep, slightly, on wet rocks covered with 

 algae. In dark pockets within the walls of caves, w^here compact 

 groups of chitons may be found, they may be seen, if watched 

 carefully, to move sHghtly upon one another; such places are, 

 however, decidedly damp. When the tide comes in and covers 

 a chiton, it may become active immediately. Conversely, 

 when left by the receding of the tide, a chiton usually stops creep- 

 ing and remains w^here it happens to be. If, however, water be 

 splashed over it, it will continue creeping for a longer time; if 

 the splashing be stopped, the animal stops creeping immediately. 



Even when left in the sun to dry, upon the tide's falling, 

 Chiton is not entirely immovable. In the case of the larger 

 animals, if they be partially covered by a shadow, they will, 

 even in this condition, move forward, or backward, or turn 

 slightly, so as to become more evenly adjusted with reference to 

 the light. The possibility of such movements suggested that an 



^According to Heath ('05c, p. 392), the gills of Trachydermon raymondi, 

 which employs the gill cavities as breeding chambers, may become occluded 

 during the breeding season by the 200 or more young trachydermons therein 

 sheltered (Plate, '99, Taf. 6, fig. 218); under these circumstances the lateral 

 proboscis lappets become (like the whole proboscis) much distended with blood, 

 and may then be concerned in respiration. 



