SENSORY REACTIONS OF CHROMODORIS ZEBRA 265 



surface are visible during creeping. It is possible that the 

 margin of the foot is alone concerned in active progression," at 

 least in so far as this is independent of cilia. With an indi- 

 vidual attached to the vertical wall of a glass aquarium, the axis 

 of the animal being horizontal, the lower edge of the foot some- 

 times becomes freed from contact with the glass, the creature 

 then being suspended by the attachment of the upper margin 

 of the foot; the median furrow is then plainly visible on the foot 

 surface. On such a free lower pedal margin two or three dis- 

 tinct waves may be made out at one time. These waves, retro- 

 grade in direction (as in Tectibranchs), are confined to the outer 

 margin of the foot. Similarly, in specimens resting in the angle 

 made by the vertical wall of the aquarium with its bottom, the 

 foot may be free anteriorly, being attached only at the posterior 

 end. In these cases two or three waves were observed on each 

 side of the foot at one time, the waves on the two sides having 

 neither definitely 'opposite' nor 'alternate' relations, but ap- 

 pearing to be quite independent of each other. The fact that 

 copious slime secretion occurs along the margin of the pedal 

 surface in animals anaesthetized with MgS04 or with chlore- 

 tone enables a test to be made of the adhesive properties of this 

 slime; it is not sufficiently sticky to cause the attachment of the 

 foot to a glass rod, although in the unanaesthetized nudibranch 

 such attachment is readily demonstrated. These several lines 

 of evidence agree in pointing to the essentially muscular, non- 

 ciliary, nature of the act of creeping in Chromodoris. It should 

 be noted that the marginal pedal waves are retrograde, not 

 direct, as Vies states for Doris. 



The direction of progression is always anterior. On a smooth 

 surface the rate of creeping in active, large animals (at 27°C.) 

 is about 1 cm. in five to seven seconds; when swimming on the 

 surface film, about half this rate. 



Although we are not concerned to give an- exhaustive account 

 of the effector systems of Chromodoris, mention may be made ol 



* In an unidentified species of Leptoplana I have observed locomotion essen- 

 tially of this kind, obviously muscular, in which the outer edge of the body was 

 the only part in contact with the substratum. W. J. C. 



