364 Vniversity of California Publications in Zoology [Vol. IS 



as the anal cirri continue to move, but as they cease to lash back and 

 forth and the animal comes to rest, the movements of the membranelles 

 also slow down. No very decided change has been seen in the rate of 

 movement of the frontal, ventral or marginal cirri. The fact that as 

 the anal cirri move there is increased activity on the part of the 

 membranelles, seems to be very significant, and this coupled with the 

 fact that there is a definite anatomical connection between these motor 

 parts, leads us to the conclusion that there is a coordination between 

 the two structures which takes place by means of the motorium and 

 connecting fibers. 



Observations also serve as a basis for attributing to the lattice-work 

 structure of the lip the function of being a tactile sense organ. It has 

 been seen that animals when swimming are very sensitive at the 

 anterior end. Their sudden reversal of movements when striking an 

 obstacle shows that they have some means of receiving tactile stimuli. 

 The facts that this structure in the lip is so closely connected with the 

 organ of locomotion as well as the organs of food getting, and that it 

 has the same chemical affinities as the other parts, show that it is a 

 part of the neuromotor system. This structural relationship and the 

 behavior of the organism seem to prove that this structure of the lip 

 serves not as an organ of motility or support, but as an organ of touch 

 for the anterior end of the body. 



As shown above, the whirling irregular movements of the frontal, 

 ventral and marginal cirri are in no way coordinated with the regular 

 rhythmical movements of the membranelles or with the backward kick 

 of the cirri. Such a lack of coordination may be accounted for when 

 it is remembered that there are thirteen cirri possessing what we have 

 called a dissociated neuromotor apparatus which is not connected with 

 the motorium or coordinating center. 



It is probable that we are dealing here Mdth a portion of the neuro- 

 motor system, which in the evolution of the organism is not yet con- 

 nected with the other central coordinating parts. Here the cytoplasm 

 has become differentiated to a certain point — far enough for the fine 

 fibrils to have formed, but not far enough for the fibrils to have become 

 condensed into a single strand like the ones connected with the anal 

 cirri. Such a system of dissociated fibers might serve to receive and 

 convey to the cirri general impulses such as are undoubtedly carried 

 over the whole cytoplasm of the organism. Such impulses stimulate 

 the cirri to move but not in such a coordinated manner as is char- 

 acteristic of the other motor parts of the animal. 



