264 W. J. CROZIER AND LESLIE B. AREY 



According to Vies ('07), no pedal waves are observable upon 

 the foot of ^olis, at least in the form of color differences, al- 

 though the direction of the pedal wave was said by him to be 

 direct, on the basis of the rippling movement seen at the edge 

 of the foot during creeping. In Doris, also, the pedal' wave was 

 said by Vies to be direct. In Tectibranchs the direction of the 

 pedal wave, well defined in this case, is retrograde (Parker, '11, 

 p. 156). The locomotion of Chromodoris is accomplished in the 

 form of a smooth, planarian-like glide. No macroscopic waves 

 have ever been seen on the foot, even when the animal was 

 swimming attached to the surface film and therefore in a very 

 favorable position for observation. Some unevenness of move- 

 ment may usually be detected along the lateral margins of the 

 foot, and, when fixed to the surface film, where locomotion is 

 very slow, gentle 'billowing' movements can usually be detected. 

 Hence it is possible, as Parker ('11) has suggested, that in this 

 case the muscular activity of locomotion is not coordinated in 

 wave form, but is arhythmic. The lateral surfaces of the body 

 and the surface of the foot are, however, richly ciliated. Much 

 slime is laid down by the foot in creeping. The possibility, 

 then, cannot be entirely excluded that progression is in part at 

 least ciliary, especially since the cilia beat in the appropriate 

 direction, namely from anterior to posterior. Small pieces cut 

 from the mantle or from the foot continue to move for several 

 days in a fixed direction about the bottom of a dish, owing to 

 the beat of the cilia which they bear. According to Olmsted 

 ('17), cilia are the means of locomotion in Marginella, Haminea, 

 and Bulla. Local muscular activity, however, shares in loco- 

 motion, for the extreme lateral margins of the foot are the re- 

 gions exerting suction when the foot serves as a hold-fast. This 

 may be seen in the cup-like puckerings along the edge of the foot 

 when 'swimming' along the surface film. These regions are not 

 sticky, as if with slime, yet to a sufficiently large surface the out- 

 line of the foot, save at its anterior end, becomes so firmly at- 

 tached that it is with difficulty pushed loose at any given point, 

 although it can be loosened instantly when the animal begins 

 to creep. Local movements of this muscular rim of the pedal 



