132 MANTON COPELAND. 



Turning now to Table II it will be seen that the average rate 

 of locomotion of Alectrion trivittata is twice as fast as that of the 

 mud snail. If one watches for a moment the two species moving 

 about in an aquarium, he does not require the use of a stopwatch 

 to be convinced of this difference. The average ciliary rate of 



TABLE II. 



Alectrion trii-illala. 



Locomotor Rate. 



Ciliary Rate. 

 (Rate at which Carmine 



(Rate at which Snails Moved a Distance of 5 Mm.). Grains u-ere Carried a 



Distance of 5 Mm. Over 

 Ciliated Foot.) 



Alectrion trivittata (2.3 seconds in eighty trials) is also faster than 

 that of the mud snail, but slower than its own locomotor rate. 1 

 The latter conclusion is based on many more trials than are 

 recorded in the table. Does this mean that some arhythmic 

 muscular operation is associated with ciliary movement and is 

 responsible for the difference between the two rates, or do the 

 cilia tend to beat faster when the snail is moving on its foot than 

 they do when it is fastened on its back? An investigation of the 

 locomotion of small pieces of the foot led me to believe 1 that the 

 latter explanation is the true one. 



The behavior of the cilia on an excised foot will be described 

 later in detail, and it is only necessary to record here that frag- 

 ments of the foot a few millimeters long move at times rapidly 

 over the substrate by ciliary action. The direction of their 

 movements, however, was so uncertain it was necessary to time 

 their speed over a distance of 2.5 mm. Some of these pedal frag- 

 ments frequently moved at the rate of 5 mm. in 1.6 seconds and 

 occasionally in 1.2 seconds, or faster than the average rate of 

 locomotion recorded for six snails in Table II. In the case of 

 these small pieces of the snail's foot there was no possibility that 

 locomotion was in any direct way brought about by muscular 

 movements. It was entirely the result of ciliary action, and 

 the resultant speed was closely similar to the usual locomotor 

 rate of the species. Under the microscope the cilia on the frag- 



