DAPHNIA; POLYPHEMUS. , 271 



another brood of eggs is seen in the cavity ; these are soon hatched, 

 and another moult takes place ; and these processes continue to 

 take place through the whole season, until the weather becomes 

 severe. All the Daphnice then seem to be destroyed ; none 

 having their existence prolonged through the winter. There is, 

 however, a very curious provision for perpetuating the race. At 

 particular seasons, the Daphnice may be found with a dark opaque 

 ^ubstance on the back of the shell. This has been termed the 

 ephippium, from its resemblance to a saddle. When examined 

 by the microscope, it is seen to be of a dense texture, and to be 

 composed of a mass of hexagonal cells ; and to contain two oval 

 bodies, which are capsules opening like a bivalve shell, each in- 

 closing an ovum covered with a horny envelope. This is first 

 seen after the 3rd moulting ; after the 4th it passes into the open 

 space in the back ; and at the 5th it is thrown off with the shell, 

 and remains floating on the surface of the water, until the tem- 

 perature rises sufficiently to hatch the eggs. The ephippial eggs 

 which are deposited in the summer are probably developed during 

 the same season ; but those which are laid in the autumn remain 

 undeveloped during the winter, being protected by their peculiar 

 envelopes ; and it is by the action of the returning warmth of 

 spring upon them, that the new generation of Daphniae is pro- 

 duced in the next year. They may be at any time hatched, how- 

 ever, by artificial warmth. " These two species of eggs," says 

 an attentive observer of the processes now described, " produced 

 by the same being, offer a very singular example in the history 

 of animals, and show with what wisdom Nature provides for the 

 preservation of even her smallest creatures." 



881. The Polyphemus has, like the Daphnia, oar-like 

 antennae, divided into two branches. It 

 is remarkable for the large size of its 

 head, which is almost entirely occupied 

 by a single enormous eye (Fig. 604). It 

 swims on its back or sides, giving to its 



antennse and le s s .<i uiek and re P eated 



motions, and executing with the greatest 

 ease all kinds of evolutions. 



