CRUSTACEA. 211 



are received into a large cavity between the back of the animal and its 

 shell, and there the young undergo almost their whole development, so 

 as to come-forth in a form nearly resembling that of their parent. Soon 

 after their birth, a moult or exuviation of the shell takes-place; and the 

 egg-coverings are cast-off with it. In a very short time afterwards, 

 another brood of eggs is seen in the cavity, and the same process is 

 repeated, the shell being again exuviated after the young have been 

 brought to maturity. At certain times, however, the Dap/Mia may be 

 seen with a dark opaque substance within the back of the shell, which 

 has been called the ephippium, from its resemblance to a saddle. This, 

 when carefully examined, is found to be of dense texture, and to be com- 

 posed of a mass of hexagonal cells; and it contains two oval bodies, each 

 consisting of an ovum covered with a horny casing, enveloped in a capsule 

 which opens like a bivalve shell. From the observations of Sir J. Lub- 

 bock, 1 it appears that the ephippium is really only an altered portion of 

 the carapace; its outer valve being a part of the outer layer of the epider- 

 mis, and its inner valve the corresponding part of the inner layer. The 

 development of the ephippial eggs takes-place at the posterior part of the 

 ovaries, and is accompanied by the formation of a greenish-brown mass 

 of granules; and form this situation the eggs pass into the receptacle 

 formed by the new carapace, where they become included between the two 

 layers of the ephippium. This is cast-off, in process of time, with the rest 

 of the skin, from which, however, it soon becomes detached; and it con- 

 tinues to envelop the eggs, generally floating on the surface of the water 

 until they are hatched with the returning warmth of spring. This curious 

 provision obviously affords protection to the eggs which are to endure 

 the severity of winter cold; and an approach to it may be seen in the re- 

 markable firmness of the envelopes of the ' winter eggs ' of some Eotifera 

 ( 451). There seems a strong probability, from the observations of Sir 

 J. Lubbock, that the * ephippial ' eggs are true sexual products, since 

 males are to be found at the time when the ephippia are developed; whilst 

 it is certain that the ordinary eggs can be produced'non-sexually, and 

 that the young which spring from them can multiply the race in like 

 manner. The young produced from the ephippial eggs seem to have the 

 same power of continuing the race by non-sexual reproduction, as the 

 young developed under ordinary circumstances. 



6 LO. In most Entomostraca, the young at the time of their emersion 

 from the egg differ considerably from the parent, especially in having 

 only the thoracic portion of the body as yet evolved, and in possessing 

 but a small number of locomotive appendages (see Fig. 411, C-G); the 

 visual organs, too, are frequently wanting at first. The process of devel- 

 opment, however, takes place with great rapidity; the animal at each 

 successive moult (which process is very commonly repeated at intervals 

 of a day or two) presenting some new parts, and becoming more and 

 more like its parent, which it very early resembles in its power of multi- 

 plication, the female laying eggs before she has attained her own full 

 size. Even when the Entomostraca have attained their full growth, they 

 continue to exuviate their shell at short intervals during the whole of 

 life; and this repeated moulting seem to prevent the animal from being 

 injured, or its movements obstructed, by the over-growth of Darasitic 

 Animalcules and Confervae; weak and sickly individuals being frequently 



1 An account of the two methods of Reproduction in Daphnia, and of the 

 structure of the Ephippium,' in " Philosophical Transactions," 1857, p. 79. 



