262 JouRNAL OF COMPARATIVE NEUROLOGY. 
vation (8, 1894) on Lumbricus that the contraction of the worm 
on stimulating any part of the body does not extend beyond 
the segment where the ventral nerve cord has been severed. 
But this severing of the musculature involves considerable in- 
jury, especially to worms like the Sabellide and Aphrodite, 
and to avoid this we ascertained by severing the nerve cord and 
stimulating the worms anterior and posterior to the cut that 
the contraction with which we had to do in our experiments 
never passes beyond the segment where the cord is cut, either 
in the postero-anterior or the antero-posterior direction. This 
fact makes the operation unnecessary, and it was therefore dis- 
pensed with in the subsequent work. 
Owing to the necessity of having the fixation points, that 
is, the points of application of the two pairs of electrodes, close 
enough together to prevent the preparation from breaking off 
when being stimulated, the actual distance between the elec- 
trodes could not be taken as a measure of the distance of nerve 
cord traversed by the impulse. At the end of the experimen- 
tation the segments were counted and the distance measured, or 
more properly estimated, the preparation being stretched as 
nearly as possible like the normally crawling worm or after it 
was killed in fresh water. The last method has this advantage 
that it gives uniform results but it may not approximate 
the true distance any closer. It goes without saying that 
neither method gives accuracy. This is especially true of 
forms with only slightly developed chitenoid epidermis like the 
Sabellidz and Glyceride and therefore capable of great elonga- 
tion and contraction. In the Nereide the distance can be mea- 
sured more accurately. In Aphrodite and Aulastomum the 
entire length of the cord was dissected out and measured. In 
addition to this difficulty of obtaining accurate measurements of 
the nerve cord other difficulties and serious sources of error 
were encountered in the experimentation, chief among these 
the activity or ‘‘spontaneous”’ contractions of the reacting por- 
tion and its unequal degree of relaxation at the moment the rec- 
ords were obtained, and the fact that the same strength of stim- 
ulus usually caused greater contraction when applied by the prox- 
