448 University of California Publications in Zoology [VOL. 19 



although the piece reverted occasionally to the spiral movement and 

 to the backward, avoiding reaction. Now, since the excised oral lip 

 reacts only in right circus movements, it would appear evident that 

 these organelles are chiefly responsible for the same movements when 

 only the three frontal cirri are added. And one may enquire whether 

 the circus movements to the right by the normal animal may not be 

 effected mainly by these adoral membranelles. The fact that when 

 such movements are performed the anal and marginal cirri not in- 

 frequently remain wholly passive, and that these movements are more 

 common after the anal and marginal cirri have been removed, would 

 lend support to such a conclusion. 



It was also observed that a sharp turn to the right was accompanied, 

 if not mainly produced, by the quick lateral flexure of the anal cirri, 

 and that when these cirri were removed, this reaction was never dis- 

 tinctly observed. 



Again, the usual reaction of the posterior part resulting from a 

 transection just anterior to the anal cirri, was a rotation with the cut 

 surface as an axis. Circus movemens to the right were infrequent 

 and still less frequent were the spiral, revolving movements on the 

 long axis. In fact, neither of these two movements was seen if the 

 marginal cirri had been snipped off previous to the transections. 



From these observations, therefore, it appears that in E. patella 

 one of the several swimming movements prevails in a piece formed by 

 a transection, or that one of these movements becomes less frequent 

 and may not appear at all upon the removal of a group of organelles. 

 such as the anal cirri. 



These facts, nevertheless, are not contradictory to the more general _ 

 truth, viz., that all the locomotor organelles cooperate in the per- 

 formance of any characteristic movement. The very significance of 

 organization precludes any other interpretation. But are we to regard 

 each group of organelles equally effective in producing any one of 

 these movements ? If so, then the removal of the marginal cirri should 

 impair a given movement in the same manner and to the same extent 

 as excision of the adoral membranelles impairs that movement. But 

 it can be said with certainty that the same results in each case do not 

 follow. Were we to assume that all the locomotor organelles of E. 

 patella function to the same end with equal effectiveness, it would be 

 necessary to regard both the adoral membranelles and the marginal 

 cirri as distinctly creeping organs, which they are not. In this respect, 

 therefore, we may speak of a division of labor among the locomotor 

 organs of E. patella. 



