Jackson, the Amphipod HyaleUa Enickerbockeri. 
67 
fishes gives a list of the species he found which had fed upon All- 
orchestis dentata (synonymous with Hyalella knickerbocker). 
Out of twelve hundred and twenty-one fishes, belonging to eighty- 
seven species of sixty-three genera and twenty-five families which 
he examined at intervals from 1876 to 1887 in various months 
from April to November, he found the following which had eaten 
this amphipod: a single white bass, eleven of the common perch, 
one of the largest darters, five young black bass, seventeen sun- 
fishes of various species, one rock bass, one pirate perch, one grass 
pickerel, six top minnows and two of the true minnows, two of 
the suckers, seventeen catfishes,—mostly young or of the smallest 
species, one dog fish and one spoon-bill (Polyodon). It will be 
seen from these statements that over 5%; of all the fish which 
Forbes examined had eaten Hyalellce. To this list of fishes I may 
add our common stickle-back. Six of these which I examined 
from Storr’s Lake near Milton, Wisconsin, had in each of their 
stomachs from one to four Hyalellce. Two stickle-backs from 
Lake Mendota, which I kept in the laboratory, seemed to prefer 
Hyalellce to almost any other food which I could give them. 
Miller’s thumbs ( Cottus ) are also known to feed upon Hyalellce, 
but their habitat is so different from that of the amphipod that 
they cannot be considered a serious enemy. Of the insect enemies 
mention may be made of the various species, both imagoes and 
larvae, belonging to the genera Ranatra, Belostoma, and Dytiscus, 
and the nymphs of dragonflies (Odonata) • 
LOCOMOTION. 
There are two distinct methods of locomotion in Hyalellas: 
crawling and swimming. When they are taken from the water 
and made to crawl upon a smooth surface, free from objects which 
they can grasp, they are very awkward; they assume a position 
with the head and the urosome bent ventrally beneath the body; 
the mid-dorsal line of the mesosome and metasome torm more or 
less of an arc of about no degrees; the weight of the body rests 
principally upon the fifth, sixth and seventh peraeopods and upon 
the gnathopods; movement is brought about to a certain extent 
by means of the third and fourth pairs of peraeopods which are 
used as walking legs, but more by the extension of the abdomen ; 
with the uropods braced against the surface upon* which the amphi- 
