Polychoerus carmelensis — Armitage 
209 
evidenced by the gathering of the worms on the 
lighted side of the aquarium in which they were 
kept. Taxic reactions were not studied as such 
in this series of experiments, but the experi- 
ments on diurnal rhythm demonstrated that the 
animals were negatively phototaxic at high light 
intensities and showed no response at low in- 
tensities. Thus the possibility of a differential 
response to low and high light intensities exists, 
as has been found for other animals (Clarke, 
1930; Baylor and Smith, 1957). Clarke (1932) 
found that a change of illumination must rise 
above a certain threshold to be effective in caus- 
ing a reversal of phototropic signs in Daphnia. 
It was mentioned previously that worms ac- 
climated to a black background showed a lesser 
degree of choice of the black background when 
the tests were repeated. Since the animals were 
kept in darkness except while being tested, it 
seemed possible that some of the worms were 
losing their acclimated condition and perhaps 
were moving in a more random manner. There- 
fore, both the animals acclimated to a white 
background and the animals acclimated to a 
black background were illuminated with 70 ft. 
c. for 12 hr., placed in darkness for 12 hr., and 
then tested. Thirty of the animals acclimated to 
the black background came to rest on the black 
background while 8 selected the white back- 
ground. The orientation to the black background 
was highly significant (chi square =: 12.6, p 
< 0.001). Nineteen of the animals acclimated 
to the white background came to rest on the 
white background and 19 selected the black 
background. Thus it was not possible to condi- 
tion the animals to select the white background 
under 70 ft. c. of light under the conditions of 
the experiment. However, the animals accli- 
mated to the black background responded al- 
most to the same degree as in the original test. 
This experiment suggests that failure to main- 
tain an orientation to a white background at 70 
ft. c. is a result of animals more sensitive to 
light changing their orientation from the white 
background to the black background. 
FEEDING BEHAVIOR 
Five P. carmelensis were placed in a Syracuse 
watch glass with a dozen copepods, Tigriopus 
calif ornicus. One of the copepods came to rest 
near the left anterior end of a Polychoerus which 
had stopped crawling. The anterior end of the 
worm was raised and with a sudden whiplike 
movement it was brought down over the Ti- 
griopus. The worm assumed a cup-shaped posi- 
tion over the copepod. The copepod was quickly 
engulfed and its movements inside the body of 
the worm could be observed. These movements 
continued for 10 min. The capture of the crus- 
tacean by Polychoerus was similar to the man- 
ner of prey capture by the acoel Convoluta par- 
adoxa (Jennings, 1957). Dead Tigriopus were 
not ingested. 
CONCLUSIONS 
1. P. carmelensis can tolerate salinity condi- 
tions ranging from 75 to 125 per cent s.w. in- 
definitely. Worms were quickly inactivated at 
concentrations of sea water above and below 
these values. Animals kept in 50 per cent s.w. 
for 5 hr. and transferred to 100 per cent s.w. 
recovered normal activity by 16 hr. after trans- 
fer. 
2. P. carmelensis was acclimated to 75 per 
cent s.w. and survival time was increased at the 
range of salinities tested over controls acclimated 
to 100 per cent s.w. 
3. There was no evidence of a diurnal or tidal 
rhythm of activity. Worms tended to be ne- 
gatively geotaxic in quiet water at low light 
intensities and positively geotaxic in agitated 
water or at high light intensities. 
4. Photokinesis, measured as the amount of 
activity in a population of worms, was linearly 
related to light intensity over the range of light 
intensities used. Only slight differences were 
found in the rate of crawling of worms over a 
measured course under highly different inten- 
sities of light. 
5. At 15 ft. c. light intensity, worms collected 
from tide pools with white shell and rock chose 
the white background when placed in a petri 
dish with half the bottom painted white and 
the other half black. Worms were acclimated 
for 96 hr. in dishes painted black and in dishes 
painted white. The black-acclimated worms 
chose the black background and the white-accli- 
mated worms chose the white background when 
tested in the petri dish with contrasting back- 
grounds of black and white. The reaction was 
