ARTICULATA. 107 
readily move from one part of the fish to another, going either backwards 
or forwards ; or leaving the fish, they swim freely through the water. In 
dissecting them, Pickering and Dana found no blood in the stomach at any 
time, whence they conclude that the food is the mucus upon the surface of 
the fish. The cylindrical egg tubes of the female are in some species 
several times the length of the body in this family, the eyes forming a single 
row. The integument is renewed periodically. The following genera 
belong to different sub-families. 
Ergasilus (pl. 78, fig. 29), which is parasitic in the gills of fishes, bears 
a considerable resemblance to Cyclops (fig. 27). They are of a minute 
size, and when they leave the egg, they have three pairs of swimming feet. 
The male has not yet been detected. 
Phyllophora (P. cornuta, pl. 78, fig. 28) is remarkable for certain dorsal 
scale-like appendages somewhat analogous to those of the Annelides, as 
Aphrodite. The single species known is found at Tongatabu. 
Orver 3. Brancutopopa. This order includes a considerable number of 
marine and freshwater species, generally of small size, the head distinct, the 
eyes generally close to the median line, and often in contact, and apparently 
single, giving rise to the names Cyclops and Monoculus. They swim freely 
through the water, either with a uniform motion or by a series of jerks, the 
organs of motion being the feet, tail, and more rarely the antenne. ‘They 
have a pair of mandibles, one pair of foot-jaws, and an upper and lower lip. 
Some authors, who consider this group to be of a higher value than an 
order, divide it into orders and other sub-divisions. The families here 
given (except the Cypridide) admit of a further division into sub-families, 
groups which are sometimes considered to be families. 
Fam. 1. Cyclopide. Cyclops (pl. 74, fig. 38) is a freshwater genus in 
which the body is pyriform, and tapering posteriorly ; the head not distinctly 
separated from the thorax, and having the eye near the anterior extremity. 
The superior or larger pair of antenne are used to assist in locomotion, and 
they vary in the two sexes, being usually shorter in the male, besides differing 
in other characters. Some of the marine species are phosphorescent. The 
freshwater species inhabit stagnant water and springs, where they may be 
seen with the naked eye jerking themselves through the water, if looked for 
attentively. The females may be distinguished by the large pair of egg 
sacs (pl. 78, fig. 27) when these are present. The young undergoes a 
metamorphosis, which lasts about twenty days. Jurine, who has published 
an elaborate work upon these microscopic creatures, cut off about two 
thirds of the antenne of a female Cyclops, but observed no change in the 
mutilated organ until the animal moulted, when both antenne appeared 
alike perfect. Inhabiting ponds which often disappear by desiccation, these 
animals and those of the neighboring families reappear with the first rain, 
having doubtless remained in the mud or damp earth. When removed 
from water and dried fifteen or twenty minutes, but few survive, and none 
when the interval of dryness reaches twenty-five minutes. They will 
recover their activity after having been thoroughly frozen. They are 
carnivorous, and when other food is not at hand, they devour their own 
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