Holmes ’ Tropisms of Animals. 
17 
scious decision on the part of the animal. The movements of the 
larva appear little more voluntary than the precise movements of 
certain protozoa or the swarm spores of algae. Let us pass to 
animals somewhat higher in the scale of life. 
Some years ago when on the Atlantic coast at Woods Hole, 
Mass., I studied the behavior of various amphipod Crustacea of 
that region and particularly the reactions of the terrestrial species 
commonly called sand fleas. It is a somewhat curious circum¬ 
stance that the aquatic amphipods are negative to light and tend 
to keep in the darkest part of their environment while the terres¬ 
trial ones are usually positive. Positive phototaxis is the most 
pronounced in the most terrestrial of the species, the large Tal- 
orchestia longicornis which lives in holes in the sand high up on 
the beach. When dug out of the sand these crustaceans usually 
lie curled up in a death feint, but when they become active they 
manifest a very strong tendency to hop toward the light. When 
brought into a room they may keep hopping toward a window 
with intervals of rest during the entire day. If they are placed 
in a dish one half of which is shaded while the other half is exposed 
to the direct sunlight they will keep hopping toward the light until 
they are overcome by the heat of the sun’s rays. 
The smaller Orchestia agilis which lives nearer the water’s 
edge and frequently manifests a negative reaction to light shows 
the same fatal degree of positive phototaxis when exposed for 
some time to strong sunlight. Does light orient these forms auto¬ 
matically and involuntarily as is apparently the case with the 
larvae of Arenicola? There are several facts which favor such 
an interpretation. The .persistent and apparently unreasonable 
nature of the response,, its sudden reversal by certain external 
agents, and especially the fact that the witless creatures continue 
to go toward the light even when they are brought thereby into a 
region where the light proves fatal to them, seem to bear out the 
conclusion that the phototaxis of these animals is in the nature of 
an involuntary or “forced” response. This view is strengthened 
by the results of certain experiments on individuals which were 
blinded on one side. These experiments were undertaken with 
the view of ascertaining something of the mechanism of orienta¬ 
tion. The amphipods do not become oriented by bending the body 
toward the light, but by the unequal activity of the appendages on 
