ORDER BRANCHIOPODA. 113 



louse, which is not produced from the fish, but from the 

 mud." It resembles a wood-louse, but the tail is larger. 



ORDER VI. BRANCHIOPODA. 



This order has for its characters the mouth composed of 

 an upper lip, two mandibles, a tongue, one or two pairs of 

 maxillae, and branchiae always placed anteriorly. These 

 Crustacea are always wandering in their habits, not being 

 parasitic upon other animals, as is the case with the order 

 Pcecilopoda. They are generally covered with a shield-like 

 shell or a case resembling a bivalve; they are furnished 

 with two or four antennae ; their legs are formed for swim- 

 ming, varying in number, some having only six, others from 

 twenty to forty-two, whilst some have more than a hundred ; 

 many have but one eye. They formed in the system of Lin- 

 naeus the single genus Monoculus, but a more precise study 

 of these animals has proved that they present modifications 

 in their structure much more striking than are to be found 

 in the large Decapod Crustacea. My friend, W. Baird, Esq., 

 has published a series of papers on these insects in Jardine's 

 Magazine of Zoology and Botany. 



This order is divisible into two principal sections ; first, 

 the LOPHYROPODA, in which the number of legs never ex- 

 ceeds ten, with cylindric or conical joints ; the branchiae are 

 few in number. Many have but one eye, and the antennae, 

 which are generally four in number, are employed as locomo- 

 tive organs. Latreille divides this first section, which is com- 

 posed of very minute species, into three principal and very 

 natural groups. 



1. The Carcinoida (Copepoda Strauss,) have the shell 

 oval or ovoid, not bivalve ; the legs are ten in number, and 

 the eggs are borne by the females in two large exter- 

 nal sacks on each side of the base of the abdomen. (Cy- 

 clops, the water flea, &c. &c.) These little creatures, which 



