No. 403.] REVIEWS OF RECENT LITERATURE. 603 
We note several American stragglers: the robin, of course, Swain- 
son’s thrush, yellow-billed cuckoo, several Waders, and the American 
bittern, appearing strangely as Botaurus freti-hudsoni (Briss.). 
E H 
Heliotropism of Cypridopsis. — The reactions of a representative 
of the Ostracoda, Cypridopsis vidua, to light have been studied by 
Elizabeth W. Towle. This animal, when dropped into the middle 
of a trough which is in the course of light rays from a Welsbach 
burner, may move either toward the source of light or away from it. 
Observation of individuals shows that an animal may at one time be 
positive, at another negative. One cause of this variation is found 
to be “contact.” For, however strongly negative an animal may be, 
it can be rendered positive by being repeatedly taken up in a pipette 
or by disturbance of the water. 
If while a Cypridopsis is moving toward the light the burner. be 
shifted to the opposite end of the trough, the animal will immediately 
turn and follow it, thus keeping up a positive reaction. Likewise, 
if it is moving away from the light it may be observed to change its 
course each time the light is moved, or, in other words, to maintain 
its negative reaction. The only difference is this : “ In all cases the 
positive response was temporary, while the negative one persisted as 
long as the animal could be kept in motion.” Contact with the sides 
of the trough or pipette or with obstructions therein causes a change 
from negative to positive; whereas the change from positive to nega- 
tive occurs independently of external conditions. 
Miss Towle’s experiments indicate that Cypridopsis cannot be 
characterized as positively phototactic, and the use of an India-ink 
prism as a means of getting regular gradations of light intensity led 
her to conclude that a photopathic reaction (Ze., a response to dif- 
ference of intensity of adjacent rays and not to the direction of 
the same) has of been proved thus far for any animal, and probably 
does not exist. As a result of careful tests with the prism she decides 
that “the direction of movement of Cypridopsis and of Daphnia in 
response to light does not result from an effort on the part of the 
animal to reach a certain optimum intensity. It is determined (1) 
by the direction of the impinging rays, and (2) by the relative value 
of these rays as forces acting upon the organism, 7.e., by their rela- 
tive intensities." 
tA Ra in the Heliotropism of Cypridopsis, Amer. Journ. of Phys., vol. iii 
(1900), No. 
