DAPHNIA; POLYPHEMUS. ORDER OSTRAPODA. 269 



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 temperature rises sufficiently to hatch the eggs. 

 The ephippial eggs which are deposited in the summer are pro- 

 bably 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 gene- 

 ration of Daphnias is produced in the next year. They may be at 

 any time hatched, however, 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." 



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

 antennse, 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. 494.) Jt 

 swims on its back or sides, giving to its 

 FIG. 494,-poLYpHKMus antennae and legs quick and repeated 



STAONORUM, magnified. . , . . , , 



motions, and executing with the greatest 

 all kinds of evolutions. 



SECTION D. ENTOMOSTRACA. 



ORDER VIII. OSTRAPODA. 



807. We are now arrived at the last group of Masticatory 

 Crustaceans; in which we lose all trace of organs peculiarly 

 adapted for respiration, the feet not being modified for this 

 purpose, as in the last Section, but being expressly formed for 

 swimming, each member being terminated by two oars composed 



