1913] 
Pearse, Notes on Eubranchipus dadayi. 
Ill 
thus agreeing with other representatives of this genus (Holmes, 
’to; McGinnis, ’ 11 ; Howland, Ti). They sometimes reacted to 
moving objects above the water by darting to the bottom of the 
dish, but were frequently indifferent. In nature the males swam 
everywhere without regard to shadows, but females showed a ten¬ 
dency to remain in shaded situations, such as the underside of 
sticks, when above the bottom of the pool. McGinnis (Ti) found 
that Eubranchipus serratus (when tested in the laboratory) 
avoided shadows and remained in the light, even when there was 
only a narrow illuminated band through an aquarium. 
Like all fairy-shrimps, Eubranchipus dadayi shows marked 
sexual dimorphism. In the males the second antennae are two- 
segmented and form Y-shaped clasping organs; whereas in the 
female these appendages are short, conical, and consist of one seg¬ 
ment. Furthermore, females are readily distinguished from males 
by the large egg sac which projects from the ventral surface of the 
body just back of the swimming appendages; a pair of small ap¬ 
pendages, the copulatory organs, occupy a similar position in the 
male. Sexual dimorphism is not limited to differences in form only. 
The color of the sexes is characteristic and different. Males have 
a delicate translucent, almost transparent, creamy color, with red¬ 
dish cercopods at the posterior end and white testes in the middle 
of the body. Females are reddish throughout. Both sexes may 
show more or less iridescent greens and blues, which are appar¬ 
ently “refraction colors,” not due to specific pigments, and these 
are usually more intense and striking on the deep red background 
of the females. Packard (’78) speaks of red and white phases of 
Eubranchipus vernalis which may occur in either sex, but the 
writer examined more than a hundred and fifty specimens of 
E. dadayi without finding a “white” female or a red male. 
The difference in color between the sexes is associated with 
difference in behavior. McGinnis (Ti) found that Eubranchipus 
serratus was “positively geotropic in light and negatively geo¬ 
tropic in darkness,” and the same is true in a general way of 
E. dadayi, when tested in the laboratory. Males are, however, 
less definite in their geotropic reactions than females, and though 
they often remained at the bottom in holes between the leaves for 
hours at a time, they commonly swam at the surface of the water 
