AND THE LOWER ANIMALS. 99 



into a few long segments, and carries anteriorly two 

 free antennse, and laterally two other appendages 

 of a similar nature inclosed in liorny cases. Three 

 pairs of feet clothed with long stout hairs answer the 

 purpose of oars. A carapace, composed of a single 

 piece, covers the back, and laps over the body ante- 

 riorly and laterally, disclosing a single solitary eye in 

 front. The little balsenus being thus provided with 

 sense-organs and locomotive apparatus, swims rapidly 

 through the water, reminding us forcibly of the larva 

 of a cyclops.* 



A change is now undergone, and the creature re- 

 sembles a cypris or an adult limnadia.f Its body is 

 entirely concealed by a pair of valves like those of 

 acephalous mollusksjj the number of feet increases; 

 and by the aid of two anterior appendages, which 

 spring from the shell, it is enabled to attach itself 

 to seaweeds and other submarine bodies. It is by 

 grasping the rock with these peculiar organs that the 

 little crustacean fixes itself in some position where the 

 waves beat most violently; it then loses its bivalve 

 shell, and replaces it by several distinct pieces, which, 

 like so many plates, cover the back and sides of the 

 animal. This, however, is essentially a transitory 

 condition. A sort of calcareous wall is very soon 

 raised around this species of nymph, and assumes the 



form of an irregular hollow pyramid, with a wide and 

 * 



# The Cyclops is a small crustacean of an inferior order, which is 

 common enough in certain fresh- water ponds, &c, and which also 

 undergoes metamorphoses that have been known for a long while. 



t The Cypris and Limnadia are small fresh- water Crustacea also. 



% The oysters, scallops, mussels, &c. ; in fact all mollusks whose 

 shell is composed of two valves united by a hinge, belong to this 

 group, of which we shall say more hereafter. 



H 2 



