These animals awim with more or less rapidity in the still fresh waters or gently-running streams which they inhabit, in proportion as they bring into action the filaments of the antennae; sometimea they only show one, at others they put them all forth. Latreille thinks that these filaments may also assist in respiration. The two anterior feet are moved with the same rapidity as the antenna when the animal is awimming ; when it creeps over the surface of the water plants, the progress ia slow. The female deposits her eggs in a mass, fixing them by means of a glutinous substance on the water-plants or on the mud. Anchored by her second pair of feet, so as to be safe from the agitation of the water, she ia occupied about two hours in this operation, the produce of which, in the largest species, amounts to 24 eggs. Jurine collected some of these at the time of their exclusion, and, after having insulated them, obtained another generation without the intervention of the male. A female which laid her eggs on the 12th of April changed her akin six timea between that day and the 18th of May following. On the 27th of the last-named month she laid again, and, two days afterwards, made a second deposit. Jurine concludes that the number of moults in the young state corresponds with the gradual development of the individual. Deamarest considers that they do not undergo a metamorphosis, but that they present on their exclusion from the egg the form which they preserve throughout their life. Their food is said to consist of dead animal substances and of amferrce. In summer, when the beats have dried up the pools, they plunge into tho humid mud, and there remain in an apocryphal kind of existence till the rains again restore them to activity.
The recent species are numerous ; Jurine described 21. Dr. Baird describes 15 species as British.
The hard shells of Cypris resist decomposition, hence many are fossiL Cypris Faba, Deamarest, holds a place among the organic remains of the Wealden Rocks of England. Dr. Fitton has recorded it in the Weald Clay of the Isle of Wight, Swanage Bay, &c., and Dr. Manton Valves brown, kldney.shaped, covered with fine scattered hairs. Antenote with fifteen fine bristles. In the view the valves are supposed to be removed, the outline e e showing their shape and their relative situation ; b, origin of the hloge membrane ; c, eye ; d d, outcome deprived of their bristles ; e, feet of the first pair ; J, of the second pair ; g, of the third pair ; h, tail ; labrum ; k, mandible; f„ feeler ; m, jaw of the first pair ; n, of the second pair ; o, bronchia or gill ; p q, posterior portion of the left ovary ; r, the male organ according to Straus.
above may account in some measure for the quantities of their petrified exuvire. Cypris has also been found in the Fresh-Water Limestone, beneath the Mid-Lothian Coal-Field, at Burcliehouse, near Edinburgh, and in other districts.
Cladocera, Latreille ; Daphnides, Straus.—These minute creatures have a single eye only, and are protected by a shell doubled as it were, but without any hinge, according to Jurine, and terminated posteriorly in a point. The head, which is covered with a kind of beak-like armour, projects beyond the shell. There are two antennx, generally large, in the form of arms, divided into two or three branches placed on a peduncle fringed with filaments always projecting, and serving the purpose of oars. The feet, four to six pairs, terminated by a digitated or pectinated swimming organ, and furnished, with the exception of the two first, with a branehial lamina. Their eggs are situated on the back, and their body terminates with a sort of tail with two delicate hairs or filaments at the end. The anterior part of the body is somtimea prolonged into the form of a beak, sometimes into a shape approaching that of a head occupied almost entirely by one largo eye.
Latreille gives the following sub-genera : Polyphemus, Mfiller; Daphnia, Muller; Lynccus, Moller (Chtledorur, Leach). This division In Baird's 'Entomostraca' includes the following families and genera.
have rendered its organisation and habit. extremely well known. In the species of Daphnia one junction of the sexes fecundates the ova for many successive generations, six at least ; their moults are very frequent ; they lay at first but one egg, then two or three, and so on progressively as they advance in life till their number amounts to 58 in one species (Daphnia ',myna); and the young of the same deposit are generally of one sex, it being rare to find two or three males in a female batch, and vice versa. As the winter approaches their moults and oviposits cease, and the frost is supposed to destroy them, leaving however the eggs unharmed, which the genial spring season hatches to fill the pools with myriads of Then those who have microscopes will find ample employment for them. Every ditch, every pool, every garden reservoir, will furnish the observer with Branchiopods.
The species are numerous. The most common is the Water-Flea, Daphnia pular of Latreille, Nonoculus pulex of Mumma, Pules aguaticus arborescras of Swammerdam, Le Perroquct d'Eau of Geoffrey. Despised as this minute creature may be by those who, like the orientalists, consider size as absolutely necessary to produce grand ideas, it has fixed the especial attention of Swammerdam, Needham, Leuwenhoek, Schaeffer, De Geer, Straus, and above all, of Jurine, who, in common with other philosophers of great name, have found as much interesting information regarding the development of animal life in the admirable organisation of these animated specks as is afforded by the largest vertebrated animal (Darneu.) Section II.