PHYLLOPODA ; LIMNADIA ; APUS. 265 



with the branchial expansions of the legs. Even when the animals 

 are at rest, these last organs are seen to be in rapid motion. 

 The eggs are arranged in a mass in a cavity beneath the back of 

 the shell, or are inclosed in a common envelope, and carried in 

 one or two bunches or masses at the base of the tail (Fig. 489). 

 802. The Order PHYLLOPODA includes those Branchiopoda, 

 whose body, sometimes naked or shell-less, and sometimes 

 inclosed in a shield-like carapace or in a bivalve shell, is divided 

 into a great number of segments, nearly all of which are 

 furnished with leaf-like appendages, or gill-feet. They vary 

 considerably in their conformation ; some of them being provided 

 with a certain number of simple swimming feet, placed behind 

 the gill-feet ; but of the latter there are always at least eight 

 pairs, and sometimes their number amounts to sixty pairs. The 

 first division of the order includes those, which have the. body 

 protected by a horny shell. This is the case with the Limnadia 

 (Fig. 490), which has a bivalve shell, and bears a considerable 



FIG. 490. LIMNADIA. FIG. 491. APUS MONTAGU;. 



resemblance to the Daphnia ( 804), except in the form and 

 number of the feet; and in the Apus (Fig. 491), which has a 

 simple shield-like shell, and in which the feet are very numerous, 

 but all except the anterior ones are extremely small. These last 

 are extremely remarkable for the power which their eggs possess, 

 of retaining their vitality for several years, when the waters in 

 which they are deposited have been dried up. They inhabit 

 lakes, pools, and ditches, and are often found in vast numbers, 

 especially in the spring and beginning of the summer. They are 

 sometimes raised into the air by whirlwinds, and scattered again 



