ARTICULATA. 109 
American species. The name of the latter is changed from reteculata, as 
this has been already applied to a European species. 
Fam. 4. Apodide. This family includes Latreille’s fifth order, Phylio- 
poda, in which the body is either naked, inclosed in a bivalve shell, or with 
the head and thorax covered with a carapace. The body is divided into a 
great number of segments, most of which have foliaceous feet adapted for 
breathing, the number of which varies from eleven to sixty pair. Antenne 
two or four in number, and not adapted for swimming; eyes two or 
three. . 
Apus (pl. 78, jig. 25) has a large carapace covering nearly the entire 
body ; one pair of short antenne, and sixty pair of branchial feet. Scheeffer 
enumerated the number of pieces which enter into the composition of the 
body, and found them to amount to 1,802,604. He found that each of the 
caudal filaments in Apas cancriformis contains 480 articulations. It 
inhabits fresh water ponds, and swims equally well with the back above or 
below. It reappears in desiccated ponds in two days after a rain; and it 
has been found in ponds that have been without water for several years, 
whence it may be inferred that the eggs retain their vitality for a long time. 
They feed upon the microscopic Entomostraca, and are in turn devoured 
by frogs. 
The metamorphosis of Apus is much like that of Cyclops, Lernea, &c. 
When the young leave the egg, the body is narrowed posteriorly, the tail is 
wanting, the antennz are large, and the first and only pair of feet are 
robust, and longer than the body, thus presenting opposite characteristics 
from the adult. The length of the common European species, A. cancré- 
Sormis, is two and a half, and the breadth one and a half inches. There 
are but few species known. One has been described from the West Indies, 
one from the eastern side of the Rocky Mountains, and another from the 
Sandwich Islands. 
Branchipus pisciformis (pl. 78, fig. 26) was described under this name, 
according to W. Baird, by Scheeffer, in 1752, and was subsequently named 
Chirocephalus diaphanus, by Prévost. It has two pedunculated eyes, four 
antennee, eleven pairs of branchial feet, and there is no shield. In the male, 
the larger pair of antenne are prehensile, resembling mandibles, their base 
is large and fleshy, and the outer joint curved and cylindrical. From the 
base of these antenne arises a pair of large flexible proboscidiform organs 
with their appendages, all of which are usually rolled up beneath the head. 
In the female the large antenne have a singular structure, being short, 
compressed, bent downwards, pointed at the end, and unprovided with 
appendages. The species figured is more than an inch long, and is found in 
pools swimming upon its back. As in nearly all the Entomostraca, the 
branchial feet are kept moving continually. These animals swim with the 
aid of the tail, darting through the water like small fishes. They feed upon 
dead animal and vegetable matter. The female has an external branchial 
sac, and the young undergo a metamorphosis. 
Limnadia is inclosed in a bivalve shell somewhat as in Cypris, but the 
animal is larger, being nearly half an inch long. The American species, 
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