JENKINS AND CARLSON, WVervous Impulse in Worms. 261 
tle or no pull on the needles, for when this is the case the worm 
breaks in two. The body of the worm was secured to the 
board as before in two places: one about I to 2 cm. anterior to 
the last and the other about the same distance posterior to 
the first point of fixation, care being taken in all cases not to 
injure the nerve cord. Between the two anterior and posterior 
fixed points the body of the animal was laid open by a longitud- 
inal dorso-median incision through the body wall. The body 
wall was pinned out to either side and the exposed viscera were 
turned to one side or removed. The nerve cord was dissected 
free from the adjacent tissue and the entire musculature com- 
pletely severed near the reacting portion, so that this was in con- 
nection with the rest of the body by the nerve cord only. The 
freed portions of the nerve cord were placed on the distal and 
the proximal pair of platinum electrodes respectively, and the 
muscle was connected with the lever by means of a hook and 
thread passing over a friction wheel at the end of the platform. 
This general account applies more especially to forms like the 
Glyceride and the Lumbriconereidz, but numerous devices 
such as narcotics, decapitation, etc., had to be resorted to to meet 
the exigencies in other groups. Variations from the general 
method are noted with each group. 
The complete freeing of the nerve cord from adjacent tis- 
sues without impairing its function is extremely difficult, if not 
practically impossible, in most worms, partly because of the 
small calibre of the cord, and partly because of its more or less 
complete investment by the ventral musculature. In Nereis virens 
thenerve cord is largeand therefore comparatively easily freed ; in 
Aulastomum, Aphrodite and, to some extent, in Arenicola, the 
cord runs free in the body cavity; but with these exceptions 
we never succeeded in completely freeing the cord from the 
ventral musculature. 
The severing of the dorso-lateral musculature (the ventral 
musculature is severed by the dissecting out of the nerve cord) 
between the two points of fixation nearest the reacting portion 
was done to prevent complications by possible myelo-conduction. 
At the time, we were not acquainted with FRIEDLANDER’S obser- 
