ANNULOSA I CRUSTACEA. 237 



several generations. Two kinds of eggs occur in Daphnia. 

 In the first of these, or " summer eggs," the ova (from ten to 

 fifty in number) are deposited in an open space between the 

 valves, and are retained there until the young are ready to be 

 hatched. In the second of these, or " winter eggs," the ova 

 (generally two in number) are placed in a peculiar receptacle, 

 which is formed on the back of the carapace, and is called the 

 " ephippium " or saddle. After a time the ephippium is cast 

 off, and floats about till spring, when its contained eggs are 

 hatched by the warmer temperature of the water. 



ORDER II. PHYLLOPODA. Crustacea, mostly of small size, 

 the carapace protecting the head and thorax, or the body 

 entirely naked. Feet numerous, never less than eight pairs, 

 mostly foliaceous or leaf-like, branchial in function. The eyes 

 sometimes confluent, sometimes distinct and sub-pedunculate. 

 There are two horny mandibles without palps, and the first 

 pair of feet are oar-like, with setiform terminal appendages. 

 The remaining feet are branchial, and adapted for swimming. 



Fig. 88. Phyllopoda. Fairy Shrimp (C kirocephalus diaphanus) after Baird. 



The Phyllopods undergo a metamorphosis, the youngest forms 

 being " Nauplii." In Nebalia, however, which is the only 

 marine Phyllopod, " Zoea-stages " are superadded as well. 



The Phyllopoda are chiefly interesting from their affinity to 

 the extinct Trilobites. In the typical genera Limnadia and 

 Apus the body is protected by a carapace, which is bivalve 

 in the former and shield-like in the latter. In Limnadia the 

 carapace covers the greater part of the body, and opens along 

 the ventral margin. There are from 18 to 30 pairs of mem- 

 branaceous and respiratory feet. In Apus the carapace is 

 clypeiform and covers a portion of the abdomen ; and there 

 are sixty pairs of feet, of which all but the first pair are 

 foliaceous. Apus is gregarious, fresh-water in habit, and often 

 found in great numbers in pools and ditches in Europe. The 

 different species of Branchipus have the body unprotected by 

 any carapace, and are found in ponds and swamps in various 

 parts of the world. The various "Brine-shrimps" (Artemid) 

 are found inhabiting the brine-pans in salt-works, or occur in 



