120 University of California Publications in Zoology [VOL. 18 



come through the etherized part we are still within the limits of trans- 

 mission, but as soon as failures become frequent it is evident that the 

 limits have been approached. More refined methods may be able to 

 determine these limits closely. My records can be considered only as 

 approximations. 



One other difficulty arises in making these determinations. Sum- 

 mation of stimuli has been shown by both Straub (1900) and Buding- 

 ton (1902) for annelid muscle. Weak stimuli adding themselves 

 together will sooner or later give a contraction. There is the possi- 

 bility that, in observations on these reactions, failures have been 

 recorded, where, in reality, weak stimuli did get through. However, 

 any errors so made would be on the conservative side. 



Conclusions. The results of these experiments show that no 

 absolute limits can be set, the impulses travel short distances in the 

 cord very readily and that the longer the section of cord to be traversed 

 the greater the difficulty. In Helodrilus twenty : eight segments was 

 the limit for the distance locomotor impulses would travel in the cord 

 when the superficial nerves were anesthetized. 



DEPENDENCE ON NERVOUS SYSTEM FOR TRANSMISSION 



Problem. While the nerve cord is capable of transmitting loco- 

 motor impulses for considerable distances is it possible for the muscles 

 to carry on rhythmical movements without the aid of the nervous 

 system ? 



Discussion. If a short section of a worm containing about twenty 

 to thirty segments is prepared in such a way that it will give a record 

 of contractions of the longitudinal muscles on a moving drum, and the 

 lever is slightly weighted so the piece will be kept straight but not 

 stretched, it will be found to make rhythmic contractions. Straub 

 (1900) and Budington (1902) show this characteristic of annelid 

 muscle but disagree in the interpretation. Straub claims that strips 

 of the muscles, both with and without nerve, will give rhythmic contrac- 

 tions. However, regions of the worm from which the nerve had been 

 removed must be given several (eight) days for recuperation and then 

 they would give contractions comparable to those of the regions of 

 worm with nerve intact. Budington found that when care was used 

 to remove all nervous tissue by using only pieces of worm in which 

 the whole ventral muscle had been removed, that such pieces gave -no 

 rhythm ; while pieces containing even a small amount of nerve gave a 

 regular rhythmic curve (fig. 10). 



