Polychoems carmelensis — Arm IT AGE 
207 
TABLE 2 
Reactions of P. carmelensis to Light of Various Intensities 
(A total of 21 animals in 6 vials were tested for 3 min. at each intensity) 
LIGHT INTENSITY 
ft. C. 
NO. ON 
SIDES 
! NO. MOVING 
DOWN 
PER CENT 
MOVING 
DOWN 
HEAD 
MOVEMENT 
AT SURFACE 
LOCOMOTION 
ON 
BOTTOM 
1.7 
15 
1 
10.0 
9 
1 
37.0 
8 
3 
2 
130.0 
11 
4 
36 
3 
5 
225 
8 
7 
87 
1 
12 
400 
5 
5 
100 
16 
by assigning an arbitrary value of 5, 10, and 20, 
respectively, to each of the above responses and 
dividing the sum of the values for individual 
worms by the sum of the number of seconds 
that elapsed until the animal responded or until 
180 sec. elapsed. Animals that did not respond 
were included. This may be illustrated in the 
following equation: 
sum of arbitrary values of 
... . , response for all worms 
Activity index = £ 
sum of number of sec. un- 
til response or until 
elapse of 180 sec. for all 
worms 
The activity index will be higher if the number 
of animals responding to the stimulus increases 
or if the nature of the response is of a higher 
level or if both of these occur. The results are 
presented in Figure 2. Activity appears to be 
linearly related to light intensity over the ranges 
of light intensity studied. It is difficult to know 
if this relationship is a real one, for it might be 
an artifact of the method used to determine ac- 
tivity. However, the raw data indicate such a 
linear relationship, so that this relationship 
seems reasonably accurate. It probably does not 
exist at higher intensities, for once an animal 
has responded fully it can no longer respond to 
an increased stimulus. 
On contrasting backgrounds, planarians come 
to rest on the darker ground (Ullyott, 1936). 
This reaction was tested in P. carmelensis in the 
following manner. Half the bottom, the sides, 
and the upper edge of the sides of a 41/2 -in. 
petri dish were painted black and the other half 
of the bottom was painted white. The dish was 
half-filled with sea water and placed in a metal 
trough through which sea water circulated to 
maintain a relatively constant temperature and 
illuminated from above by 15 ft. c. of light. 
Ten (in some experiments, 20) animals were 
added to the petri dish as close to the center as 
possible. The animals were allowed 1 hr. to come 
to rest, after which the animals on each back- 
ground were counted. The dish was rotated 90° 
between trials so that if the animals were re- 
acting to light being reflected from the wall of 
the room or from the sides of the dish, such a 
directional orientation could be detected. The 
position of rest of each animal for each trial 
was plotted on a drawing of a petri dish. There 
was no evidence of directional orientation in 
any of the experiments. Forty different individ- 
uals were used in the first set of experiments. 
All animals were kept in the dark between trials. 
Any animal that crawled up on the side of the 
dish was considered to be on a black background. 
The experiments extended over 5 days. Of 40 
animals tested, 33 came to rest on the white 
background and 7 came to rest on the black 
background. The marked orientation to the 
white background (chi square = 1 6.8, p < 
0.001) was unexpected in view of the results 
with planarians. The testing was repeated four 
times using the same animals. The results were 
similar in all cases. Since all of the animals came 
from an area of broken shell, most of which was 
white, it was postulated that the animals were 
acclimated to the white background. If this 
hypothesis were correct, then it should be pos- 
sible to acclimate the worms to a black back- 
