112 CRUSTACEA. 



SECOND GENERAL DIVISION. 



ENTOMOSTRACA. 



Under this denomination, which is taken from the Greek 

 and signifies Insects with shells, Othon Frederick Muller 

 comprises the genus Monoculus of Linnaeus, to which we 

 must add some of his Lernasse. His investigation of these 

 animals, the study of which is so much the more difficult as 

 they are mostly microscopic, and the observations of Schseffer 

 and of M. Jurine, Sen., have excited the admiration and 

 secured the gratitude of every naturalist. Other but partial 

 labours such as those of Randohr, Straus, Herman, Jun., Ju- 

 rine, Jun., A. Brongniart, Victor Audouin, and Milne Ed- 

 wards, have extended our knowledge of these animals and 

 particularly of their anatomy ; but in this respect, Straus, as 

 well as M. Jurine, Sen., although preceded by Randohr in 

 the observation of several important details of organization, of 

 whose memoir on the Monoculi, 1805, they seem to have been 

 ignorant, has surpassed them all. Fabricius merely adopted 

 the genus Limulus of Muller, which he placed in his class of 

 the Kleistagnatha, or our family Brachyura of the order De- 

 capoda. All the other Entomostraca are united as by Lin- 

 nseus in one single genus, Monoculus, which he places in his 

 class of the Polygonata or our Isopoda. 



These animals are all aquatic and mostly inhabit fresh wa- 

 ter. Their feet, the number of which varies, and that some- 

 times extends to beyond a hundred, are usually fitted for 

 natation only, being sometimes ramified or divided, and some- 

 times furnished with pinnulse or formed of lamella?. Their 

 brain is formed of one or two globules. The heart has always 

 the figure of a long vessel. The branchiae, composed of hairs 

 or setae, singly or united, in the form of barbs, combs or tufts, 



