644 REPRODUCTION AND DEVELOPMENT OF ENTOMOSTRACA. 



to be composed 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. Lubbock, * 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 Epidermis, 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 from 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, in process 

 of time, with the rest of the Skin, from which, however, it soon 

 becomes detached ; and it continues to envelope 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 some approach to it may be seen in the remark- 

 able firmness of the envelopes of the ' Winter Eggs ' of some 

 Rotifera (§ 361). There seems a strong probability, from the obser- 

 vations 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. It has been ascer- 

 tained by Dr. Baird, that the young produced from the Ephippial 

 eggs have the same power of continuing the race by Non-sexual 

 reproduction, as the young developed under ordinary circumstances. 

 504. In most Entomostraca, the Young at the time of their 

 emersion from the egg differ considerably from the parent, espe- 

 cially in having only the Thoracic portion of the body as yet 

 evolved, and in possessing but a small number of Locomotive 

 appendages (see Fig. 331, c-g); the Visual organs, too, are frequently 

 wanting at first. The process of Development, 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 Multipli- 

 cation, 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 seems to prevent the 

 animal from being injured, or its movements obstructed, by the 

 overgrowth of parasitic Animalcules and Conferva? ; weak and sickly 

 individuals being frequently seen to be so covered with such para- 



* ' An account of the two methods of Reproduction in Daphnia, and 

 of the structure of the Ephippium,' in "Philosophical Transactions," 

 1857, p. 79. 



