YELLOW-BROWN CELLS OF GCONVOLUTA PARADOXA. 437 
may be-overridden by strong stimuli. Under normal con- 
ditions, whilst C. paradoxa keeps well within the region of 
a perpetual rain of powerful directive stimuli, “‘upness” will 
not manifest itself. Under abnormal conditions the habit will 
assert itself, and, on the average, to the benefit of the animal. 
(3) Background Reaction.—C. paradoxa tends to 
stick to a black ground and to move freely over a white 
TEXT-FIGURE 2.—Phototactism of C. paradoxa: the influence 
of light-intensity on phototactic response. a. Mode of response 
when the light-intensity is high. 4. Mode of response when licht- 
intensity is low. The glass troughs containing the animals are 
represented (in plan) by oblongs. The troughs standing on a black 
ground are represented by the shaded, those on a white ground by 
the clear oblongs. The animals are indicated by dots, and the arrows 
show the direction of the light. 
ground. It is probable that the sticking is due to light- 
perception by the orange-red “ glands” of the body (PI. 26, 
fis. 4 and 6), and particularly of the tail and to consequent 
reflex secretion of mucilage and activation of the stout 
bristle-like structures which, as described, project from the 
surface of the body. It is significant that the tail-like ex- 
tremity of the animal is at once richer in pigment-containing 
glands and in bristles than is the rest of the body, and that 
it is also the sticking-organ. 
