SECOND GENERAL DIVISION. 
THE ENTOMOSTRACA, Mull. 
Under this denomination, formed from the Greek, and sig- 
nifying insects with shells, Otho Frederick Muller comprehends 
the genus monoculm of Linnaeus, to which we must add some 
of his lerrmce . His researches on these animals, the study of 
which is so much the more difficult, as they are for the most 
part microscopic, and those of Schceffer and J urine the elder, 
have excited the admiration and merit the acknowledgment of 
all naturalists. Other, but more partial labours, such as those 
of Ramdolir, 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 Muller, 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 Linn se an sys- 
tem, into a single genus, that of 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 
