438 University of California Publications in Zoology [VOL. 19 



Between the two ventral a ml ju-c. anal cirri (fig. 4). Hero, the 

 movements of the anterior piece are quite similar to those of the same 

 part described just previously. There is, however, less tendency to 

 swim in circuits to the right .-mil spiral swimming movements are con- 

 siderably more frequent. Indeed, in the two respects just mentioned, 

 this part closely approximated the corresponding swimming movements 

 of the normal animal. There are, on the other hand, some notable 

 differences: (1) Avoiding reactions (swimming movement 6, p. 429) 

 are seldom observed even when the oral lip region is strongly stimu- 

 lated by means of the needle, or when some disagreeable solution, such 

 as methylene blue, is introduced. (2) Creeping is very infrequently 

 attempted and is conspicuously more or less impossible. In a few cases. 

 the piece has been observed to crawl slowly and awkwardly for a short 

 distance over-debris or along the needle, but this ability is distinctly 

 impaired. (3) Sharp turns to the right have not been seen. Tortuous, 

 random movements that involve turning both to the right and to the 

 left are sometimes resorted to but these are readily distinguishable 

 from the short, sharp turns to the right which are common for the 

 normal animal (swimming movement 5, p. 429). (4) The creeping 

 "avoiding reaction" (number 2, p. 429) has at no time been observed 

 even when mechanical stimuli are applied. 



The principal characteristic movement of this posterior piece is its 

 rotating on the cut surface as an axis, a rotation which is not uncom- 

 monly very rapid (two or three times per second) following the com- 

 pletion of a transection. This performance is of brief duration and 

 the piece comes to rest on the surface film of the hanging drop or upon 

 debris. Thereafter, it is usually very irresponsive to mechanical or 

 chemical stimuli. If aroused, its revolving movements are performed 

 chiefly by means of the marginal cirri, the anal cirri functioning 

 individually and spasmodically, or not at all. But previously, just 

 after the operation, the anal cirri were very active and mostly respon- 

 sible for the rapid revolutions. Imperfect circus movements to the 

 right and aboral spiral movements are quite uncommon for this part. 

 These have never been observed after the marginal cirri were excised, 

 as a later experiment will show. 



Experiment 160 (fig. 4). Anterior piece immediately swims in circus move- 

 ments to right, but as often or more often moves in aboral spiral straight ahead. 

 Sometimes performs winding, devious movements but returns to spiral swimming 

 or to circus movements. During ten minutes it reversed three times to swim a 

 short distance backwards; this reaction fairly normal. Two hours later, resting 

 on d4bris. Very responsive to jar, also to needle. Oral lip much more sensitive 

 than membranelles, cirri, or any part of the body. Slowly and awkwardly 



