234 J. M. D. OLMSTED 



enough to place the whole foot in contact with the plate. This 

 is a similar result to that which Parker ('11) found with an ex- 

 hausted Helix pomatia. 



The ordinary pedal waves which carry Chiton forward are 

 composed of two bands, the first lighter in color than the rest of 

 the foot and often 1.5 cm. broad, the second following the first 

 and darker in color, usually half a centimeter in breadth. The 

 wave which carries Chiton backward moves in exactly the same 

 direction as the other, i.e. , is retrograde, but has no lighter portion. 

 It consists solely of the very dark band and is about 0.7 cm. 

 broad. It can be seen that this area is one of great contraction 

 since it may be raised from the substrate 2 mm. or more. 



For backward movement Parker's ('11) scheme holds good, 

 the only change being that the fixed point of each longitudinal 

 fiber during contraction is the posterior instead of the anterior 

 end. The wave would then travel in the same direction as before, 

 but the animal would proceed in the opposite direction. 



Experiments were also undertaken to determine whether 

 Chiton would 'back' when attached to the top and sides of 

 a vertical plate by the posterior end of the foot. The weight 

 of the body seemed to influence the reactions in both cases. 

 When attached to the side, the first wave only would carry the 

 foot in a straight horizontal direction, all the succeeding waves 

 carried the animal diagonally, a combination of backward and 

 turning movements. When attached to the upper edge of the 

 plate, the Chiton would bend over and attach the anterior end 

 of the foot to the other side of the plate if less than one-fourth of 

 the foot was attached. But if one-fourth or more of the foot is 

 attached, the animal will, without turning, back on to the plate, 

 covering a distance of 1.5 cm. in 4 waves. Twelve trials were 

 made where the individual was balanced across the upper edge 

 of the plate and allowed to attach as it would. Five times it 

 attached the anterior end of the foot and moved forward, seven 

 times the posterior end was attached and the animal backed down 

 the glass. In nearly every trial the Chiton would raise its 

 anterior end and thus upset the balance, causing the posterior 

 end of the foot to touch the plate. Nevertheless in nearly half 



