86 University of California Publications in Zoology [VOL. 13 



The facts which indicate a co-ordinating (i.e., nervous) function 

 rather than a contractile or a supporting function for the above de- 

 scribed structure may be summed up as follows : 



1. The size, shape, position, and absence of direct connection with 

 surrounding structures make the possibility of the motorium function- 

 ing as an organ either of contraction or of support seem highly im- 

 probable. For in order to function as an organ of contraction it 

 would necessarily need to have as its attachments on the one hand 

 structures which are fixed, and on the other structures which are 

 movable, or it would need to be located between two structures both 

 of which were to be moved. This however, is not the case, for the 

 motorium seems to have no direct connections with the fixed structures 

 of the body, nor does it lie in the direction of contraction of the 

 oesophagus and oral region, which upon retraction, descend posteriorly 

 into the body (compare figures B and D). Neither would the assign- 

 ment of a supporting function to the motorium be feasible, first because 

 of its relatively diminutive size, second because of its shape which 

 does not conform particularly to that portion of the animal in which 

 it is located, and third because of its location, i.e., it is situated in 

 the anterior flexible and retractile end of the body surrounded by the 

 nonresistant, semifluid ectoplasm. 



2. The strands which leave the operculum are likewise not at- 

 tached to fixed structures but lie in the semifluid ectoplasm of the 

 opercular region and in the inner dorsal and inner adoral lips which 

 are both highly mobile. Also it is to be remembered that both the 

 inner dorsal and inner adoral lips which are mobile are well pro- 

 tected and well supported by the outer dorsal and outer adoral lips 

 respectively both of which are fixed and rigid. 



3. There is never a translation of the parts in the direction^ of the 

 strands leaving the motorium, but rather in a direction at right angles 

 to the course of the fibers, thus militating against a contractile function 

 for the fibers. An apparent exception to this general statement is 

 to be found in the case of the oesophagus with its oesophageal fibers, 

 but here it is to be noted; first, that these oesophageal fibers end in 

 the vicinity of the micronucleus without any discoverable connection 

 with a fixed structure, and second that the oesophagus is richly sup- 

 plied with another set of fibers (the oesophageal retractor strands), 

 which do not take the red stain, and which are apparently attached to 

 the skeletal structure as described above. 



