58 Bulletin Wisconsin Natural History Society. [Vol. 10, Nos. 1 & 2. 
pod crawls, an extension of the abdomen results in a very crude 
leap forward. During the entire operation the pleopods are in 
constant motion, as they are in fact during most of the life of the 
animal. A modification of this method of locomotion is some¬ 
times resorted to by animals in the aquarium: the appendages rest 
against the surface as before and, upon extending the abdomen, 
the animal is able to leap through the water a distance of one to 
two inches. The constant movements of the pleopods aid here, 
and this means of locomotion is in reality a combination between 
crawling on a smooth plane and swimming. When the amphipod 
crawls among objects the body is not so flexed; the first antennae 
are extended, the second are employed to feel the way and occa¬ 
sionally to pull the animal along; with the gnathopods, chiefly 
the second pair, the animal grasps objects and pulls itself forward; 
the third to the seventh peraeopods have the same function as 
when it crawls on a smooth surface; the uropods push against 
objects in the rear. It is this method of locomotion to which 
Hyalellce most frequently resort in their natural habitat. They 
seldom swim in the daylight unless disturbed and then generally 
for only a short distance. At night they are more active and 
may be seen swimming everywhere in their habitat. Swimming 
is effected by the constant motion of the pleopods and the occa¬ 
sional extension of the abdomen. They swim in a series of undula¬ 
tions lying in a vertical plane. The convexity of the body tends 
to cause the animal to swim in a circle with the dorsal surface of 
the body outward. This effect is counterbalanced by the beating 
of the pleopods on the concave ventral surface. The result is that 
with each beat of the pleopods the anterior end of the animal is 
elevated, but, during the progression immediately following, the 
line of direction curves downward, due to the curvature of the 
body. 
THIGMOTAXIS. 
This species, like the majority of amphipods, is strongly thig- 
motactic. Its reaction to contact stimuli is shown in many ways. 
If a number of Hyaleila are placed in water in a glass jar where 
there are no weeds, stones,-or other objects, they at first appear 
restless, swim around, and finally come to' rest in the angles of the 
jar where the greatest amount of their body surface can be in 
