440 



CRUSTACEA. 



and two-jointed tarsu9. From the front of the head arise two very short, single-jointed antennae. The shell is so 

 transparent that all the viscera may be seen through it. The matrix, when filled with eggs, occupies the major 

 part of its interior ; but their number, even in the most numerous broods, does not 

 exceed ten. The eye is the first part of the animal which makes its appearance whilst 

 in the egg. The abdomen is terminated by a long tail suddenly folded back. The 

 animal always swims on its back or sides, giving to its antenna? and legs quick and 

 repeated motions, and executing, with the greatest ease, all kinds of evolutions. It is 

 subject, in its infancy, to the disease alluded to more in detail under Daphnia, named 

 the Ephippium (la Selle); but the Ephippium is always of a determinate shape. Kept 

 Fig. 19— Polyphemus stagnornm, j n confinement, it soon dies ; and its young do not live long after their first moultings. 



magnified. 



Jurine was not able to detect males amongst the individuals he examined, but the 

 species is rare near Geneva. It is, however, very common in the ditches and lakes of the north of France, [as well 

 as in England], where it may often be seen in considerable troops. 



[Evadnc, Loven, in Swed. Trans., 1835, differs from Polyphemus in having the head not detached from the body, 

 with the antennae (or mandibular palpi, according to Loven) bifid. E. Nordmanni. Found in the Baltic Sea.] 



Daphnia, Muller, has the antennae as long as the body, divided into two branches, of which the posterior is 

 4-jointed, the basal joint being very short ; and the anterior is 3-jointed. The eye forms a small point, and is 

 not accompanied, except in a few species, by an anterior black dot, mistaken by Muller and Ramdohr for a second 

 eye in Lynceus. Although of such minute size, the anatomy of these animals has been elaborately investigated 

 by Schaffer, Ramdohr, Strauss, and the elder Jurine, — Strauss having especially examined their structure, whilst 

 Jurine closely noticed their habits. The mouth is situated beneath, at the base of the rostrum. We consider as 

 an elongated clypeus the inferior portion of the head, termed labium by Strauss, and we apply the name of 

 labrum to the part which he terms the posterior lobule of the labrum. Beneath this are two very strong mandi- 

 bles destitute of palpi, and applied against two horizontal maxillae, terminated by three strong corneous spines, 

 like recurved hooks. Then succeed ten legs, all of which have the second joint vesiculose ; the eight anterior 

 terminated in a fin-like dilatation, with bearded filaments at its edges, arranged like a crown ; the two anterior 

 appear more especially organs of prehension. Ramdohr calls them palpi, and Jurine, hands, (as in Cyclops) ; from 

 the bearded terminal seta?, we do not see why they should not be employed in respiration*, although Strauss has 

 a different opinion. The two hind-feet have a somewhat different form. The abdomen or body is divided into 

 eight segments, perfectly disengaged within the shell, long, slender, and bent down at the tip, which is termin- 

 ated by two recurved hooks. The sixth segment has a row of tubercles, and the fourth a kind of tail. The eggs 

 remain in a large dorsal sac or matrix, between the shell and the body, for some time after they are discharged 

 from the ovaries. Muller gave the name of Ephippium (la Selle) to a long, dark-coloured spot, which at certain 

 seasons appears after the moulting of the females at the upper part of the valves of the shell, and which Jurine 

 attributes to a disease. According to Strauss, this Ephippium consists of two external plates, riveted on the back 

 by a hinge, and inclosing two oval capsules, each formed of two valves or lateral plates. Each of these capsules 

 incloses a corneous, greenish egg, similar in other respects to the common eggs, but remaining much longer un- 

 hatched, and passing the winter in this state, the Ephippium forming a defence at the time of moulting : this 

 Ephippium and its eggs are cast, and the eggs produce young, agreeing precisely with those of the ordinary eggs. 

 The eggs, according to Jurine, hatch in summer in two or three days, but they are capable of remaining for a very 

 long time in a state of desiccation. When the young, which have attained considerable developement in the ma- 

 trix of the female, are fit to be discharged, the parent suddenly deflexes the tail and they quit the pouch. [Want 

 of space prevents us from giving numerous details relative to the gradual developement of the young.] The males 

 are very different from the females ; the head shorter, the rostrum less extended, the valves of the shell nar- 

 rower and less gibbose, the antennas much larger. Strauss was unable to detect the sexual organs of this sex. The 

 two valves of the shell terminate in both sexes in a style, toothed on its under-side, curved near its base, and of a 

 length equal to that of the valves. At each moulting, however, this style becomes shorter, so that in adult indi- 

 viduals it forms merely an obtuse point. A single act of impregnation is sufficient for several succeeding (six at 

 least) generations, as proved by Jurine. About eight days after their birth, the yxmng moult for the first time, 

 and repeat the operation every five or six days, according to the state of the weather : not only the body and the 

 valves, but also the branchiae, and the setae of the oars, cast off their epidermis. It is not until the third moult- 

 ing that they begin to produce young, and at first they only lay a single egg, then two or three, the number 

 gradually increasing to as many as fifty-eight in one species (D. magna). The following day after laying her 

 eggs, the female moults, and in the shed teguments the shells of the eggs of her last brood are also found. The 

 eggs of each brood are almost exclusively of one sex, it being very rare to find two or three males in a female 

 brood, and vice versa. In five or six broods in the summer, one at least is of males. These Crustacea cease to 

 breed and to moult at the approach of winter, and are killed by the first frost. The Ephippial egss which had 

 been laid in the summer hatch in the following spring, and in a short time the ponds or ditches are again peopled 

 with an infinity of Daphnia. Many naturalists have attributed the red colour of some of these waters to the 

 presence of myriads of D.pulex ; but Strauss has never proved this fact, the species being generally but slightly 

 coloured. In the morning and evening, and even in cloudy days, the Daphniae generally station themselves on 

 the surface, but in the heat of the day they seek the depths of the water. They swim by taking short springs, 



* Strauss indeed considered Cypris and Cythere not to be real Bran- 

 chiopods, because their feet are not branchial ; but we do not see 

 why the hairs of the two anterior and of the antenure may not, as well 



as those of the palpi and anterior maxilla:, perform the office of 

 branchiae. 



