360 ■ University of California Publications in Zoology [Vol. is 



the basal granules of the cirri. Such a relationship immediately sug- 

 gests that these fibers are in some way associated with the movements 

 of the cirri. Such an association is undoubtedly true but not in the 

 sense that the fibers are contractile but rather that they serve as a 

 means by which motor impulses are transmitted from the anterior 

 coordinating center to the anal cirri, the chief organs of locomotion. 

 There is no evidence that these fibers have the function of muscular 

 elements, for in a study of hundreds of stained specimens I have 

 failed to recognize any shortening or thickening of them which would 

 indicate a contraction. It seems certain that if such a contraction 

 did occur some specimens would show it, for the killing fluids used 

 were such that death of the organism was undoubtedly instantaneous 

 and so should have fixed some of the fibers in the contracted condition. 

 A study has also been made of living animals which have been slowed 

 down by the use of very minute quantities of a solution of nicotine. 

 It is possible under proper conditions of light to see the fibers in 

 animals whose cirri and membranelles are active. In no case has there 

 been seen any evidence of a contraction of the fibers, even when the 

 motor organs are quite active. 



The criticism will probably be raised that since the fibers are 

 granular, it would be improbable that impulses would jump from one 

 granule to another. In answer to this it must be remembered tHat here 

 we are dealing with a nervous system of a very primitive sort, merely 

 a differentiated protoplasm. Since all protoplasm is granular to some 

 extent and has as one of its fimdamental characteristics the property 

 of conductivity, it is perfectly logical to suppose that some of the 

 granules have become aggregated into rows in which this fundamental 

 characteristic of conductivity is more developed than in other parts of 

 the surrounding protoplasm. Then, too, the granules are so close 

 together that a careful study under high magnification is necessary 

 to bring out the granular character of the fibers. Such granules are 

 not lying free in space but undoubtedly are held together by a differ- 

 entiated intergranular protoplasm, thus forming a complete continuous 

 path over which impulses might pass. 



Thus having established a path over which impulses may pass, it 

 is important to see how such impulses may be transferred to the 

 motor organs and how such motor organs may move when stimulated. 



We have seen in the above descriptions that the fibers break up 

 and come in direct contact with the basal granules of the cirri. This 

 forms a basis for attributing to the basal granules the function of 



