SECOND GENERAL DIVISION. 



THE ENTOMOSTRACA, Milll. 



Under this denomination, formed from the Greek, and sig- 

 nifying insects with shells, Otho Frederick Miiller comprehends 

 the genus monoculus of Linnasus, to which we must add some 

 of his leni(Ecs. His researches on these animals, the study of 

 \\'hich is so much the more difficult, as they are for the most 

 part microscopic, and those of Schceffer and Jurine the elder, 

 have excited the admiration and merit the acknowledgment of 

 all naturalists. Other, but more partial labours, such as those 

 of Ramdohr, Straus, Herman the younger, Jurine the younger, 

 Adolphe Brogniart, Victor Audouin, and Milne Edwards, have 

 extended our knowledge of these animals, especially in anato- 

 mical points ; but in this respect, M. Straus, — though antici- 

 pated, as well as the elder Jurine, as to many important facts 

 of organization by Ramdohr, whose memoir on the monoculi, 

 published in 1805, they do not seem to know, — has surpassed 

 them all. Fabricius has confined himself to the adoption of 

 the genus limulus of Miiller, which he has placed in his class 

 of Kleistagnatha, or our family of brachyura, order decapoda. 

 All the other entomostraca are united, as in the Linnsean sys- 

 tem, into a single genus, that o^ monoculus, which he places in 

 his class of polygonata, or our isopoda. 



These animals are all aquatic, and for the most part in- 

 habit the fresh waters. Their feet, the number of which varies, " 

 and in some exceeds an hundred, are in general adapted only 

 for swimming, and sometimes ramified or divided, sometimes 



