JENKINS AND Car son, (Vervous Impulse in Worms. = 271 
layer, while that of the posterior portion is comparatively little 
developed and is feeble in its action. On the other hand, the 
contraction of the anterior portion was quick and powerful, 
readily lifting a weight of 1000 grams. Consequently while 
the preparations allowed the determination of the postero-an- 
terior rate in the cord, the antero-posterior rate was not ob- 
tained. 
On account of the difficulties in dissecting out the cord 
and the chances of injury to it on approaching it through the 
dorsal side, the nerve-cord preparation in this worm could not 
be made in the same way as was done in the other worms. It 
was treated as follows: The worm was pinned to the board dor- 
sal side down; a longitudinal incision was made through the 
body wall on each side about one mm. from the median line on 
the vental side; this ventral strip was further freed from all con- 
nection with the organs in the body cavity. This strip con- 
taining the uninjured ventral cord was raised and placed on the 
electrodes. While this method, used with care, kept the cord 
uninjured, it presented the apparent disadvantage of placing a 
comparatively large thickness of tissue between the cords and 
the electrodes. This did not, however, prove of any disadvan- 
tage, as vigorous responses were obtained from single break in- 
duction shocks even on stimulation at the posterior point, when 
the secondary coil was 24 cm. fromthe primary. The anterior 
12 to 15 segments were used as the reacting portion, leaving 
from 17 to 20 cm. of nerve-cord between the points of stimulation. 
The lever was weighted with from 20 to 25 grams. Ai single 
break induction shock produces a single prolonged contraction. 
The preparation is not easily fatigued. Anaesthetics were 
found not to be necessary. The length of the nerve used was 
measured after the preparation was killed in fresh water. Their 
length, thus killed, corresponds to that of the animals undisturbed 
in the aquarium but freed from their tubes. In this condition the 
worm is from 12 to 15 cm. shorter than than in its tube. 
EXPERIMENT No. 10, Table V, postero-anterior, temp. 14°C, Jan. 2, 1902. 
Distal Proximal 
No. of records II 7] 
Mean latent time 0.057 sec. 0.024 sec. 
Standard deviation 0.0022 sec. 0.002 sec. 
Coefficient of variability -04 .08 
Length of cord: 20 cm. (150 segments). Rate: 606 cm. per sec. 
