ARTICULATA. 107 



readily move from one part of tlie 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 difierent sub-families. 



Ergasilus {pi. 78, jig. 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 o.^^.^ they have three pairs of swimming feet. 

 The male has not yet been detected. 



Fliyllophoixi {P. cormita., pi. 7S,fig. 28) is remarkable for certain dorsal 

 scale-like appendages somewhat analogous to those of the Annelides, as 

 Aphrodite. The single sjjecies known is found at Tongatabu. 



Okder 3. Branchiopoda. 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 Cyclojjs and Monoculiis. Tliey 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 antennae. 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 Cyprididce) admit of a further division into sub-families, 

 groups which are sometimes considered to be families. 



Fam. 1. Cydopidce. Cyclops {pi. 74, fig. 33) 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 antennae 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 {2)1. 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 oif about two 

 thirds of the antennae of a female Cyclops, but observed no change in the 

 mutilated organ until the animal moulted, when both antennse 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 wall 

 recover their activity after having been thoroughly frozen. They are 

 carnivorous, and when other food is not at hand, they devour their own 



311 



