1897] Zoology. 621 
a photometer for each experiment. Diffuse light was cut off from the 
trough by placing this in a second trough with high walls. 
The Daphinz were introduced one at a time at the end of the trough 
most distant from the light and the time noted when they passed a 
point 2 cm. from the end of the trough, and again when they passed 
another point two centimeters distant fromthe other end. The differ- 
ence then equalled the time of the trip. 
Six series of experiments were performed which were divided into 
two groups. In the first group there was an alternation from full light 
to one-fourth light to full light again, and in the second group, from one- 
fourth to full to one-fourth light. 
The distance travelled was 16 cm. The mean times in seconds found 
in the three series of the first group was 48 (full light), 57, (4 light), 
and 31 (full light). In the second group it was 36 (4 light), 28 (full 
light), and 30.5 (4 light). The average time for the full light was 35.7 
and for + light 41.2, or expressed as a ratio of the former to the latter 
the time was 87: 100. 
Sixty trips made in the order of the averages just given in experi- 
ments with several individuals changed the ratio to 84: 100. 
The Diaphniz acted differently when first put inthe trough. In full 
light they started immediately, but in one-fourth light they evinced 
hesitating movements. This together with the absence of any close 
relation between the diminished intensity of light and the longer time 
required for migration in such light than in full light as shown in the 
averages obtained the authors conclude, and it seems justly, that the 
longer time required to migrate in the smaller amount of light is due 
not so much to the lower intensity as to diminished precision in orienta- 
tion. And this leads to the further conclusion already reached in other 
experiments that light acts chiefly through the direction of its rays. 
The authors’ results bear out the conclusions of Nägeli (78) and 
of Strasburger, who says that the course of swarm spores is straightest 
in those areas that are brighest, as well as those of Loeb, who asserts 
that “the orientation of an animal in ea direction of the rays is the 
more precise as the intensity increases.” 
The table of figures showing the time of the several trips brings out a 
further fact, namely, that the rate of movement increases with each 
Succeeding trip made by the same animal. The succession averages 
for full light were 48, 31, and 28 seconds, and those for one-fourth light, 
57, 36, and 30.5 seconds. The cause of this increase of speed the authors 
say they must leave undetermined, but it would seem from common ex- 
perience that it may have been and probably was due to the animals’ 
