History of British Entomostraca. 39 
for the most part, enclosed within a testaceous covering, either in 
the form of a buckler, or that of a bivalve shell. The second order 
Paecilopoda embraces those insects which are not provided with or- 
gans proper for mastication, and are almost all parasitical, living upon 
fishes and other aquatic animals. The first order, the Brancho- 
poda, is divided into two principal sections, the " Lophyropa and 
Phyllopa." The first of these again is subdivided into three very 
natural groups or families, the " Carcinoida, Ostracoda, and Clado- 
cera ;" while the second is subdivided into two. The Paecilopoda, 
on the other hand, is composed of rather heterogeneous materials, and 
many of the genera approach very much to the " Lerneae," though, 
according to Latreille, the presence of eyes, the faculty of changing 
their skin, or even of undergoing a species of metamorphosis, and the 
power which they possess of transporting themselves from one place 
to another, by means of feet, establish a positive line of demarcation 
between the Paecilopoda and Lerneae.* The arrangement above- 
mentioned has, since 1829, received from its accomplished author, 
some modifications, which he published in 1831, in his et Cours 
d' Entomologie," but which I have not seen. The last writer upon 
the Crustacea, M. Milne-Edwards, in his work, half of which 
only is as yet published, t has taken perhaps a more philosophical 
view of the subject, and has proposed the following arrangement : 
The great class " Crustacea" he divides into three sub-classes, the 
characters of which are taken chiefly from the organization of the 
mouth. The two first of these have an apparatus especially 
provided for the laying hold of the substances destined for their 
food, while the third has no such special organization, their masti- 
catory organs being the same as their organs of locomotion. The 
first sub-class is that of the MaxilUs or those whose mouth is 
furnished with organs for mastication, the second is that of the 
Suceurs, or those whose mouth is furnished with an apparatus for 
sucking, and the third is that of the Xyphosuriens, or those whose 
organs of motion are the same as the organs of mastication, and 
which differ in many other points also from the two first. The sub- 
class Maxilles, he again divides into four legions, 1st, " Podop- 
thalmiens," containing the orders " Decapodes" and " Stomapodes ;" 
2d, " Edriopthalmes," containing the orders, " Amphipodes," " Iso- 
podes," and " Lamipodes ;" 3d, " Entomostraces," containing the 
orders "Ostrapodes," and" Copepodes ;" and 4th, " Branchiopodes," 
containing the orders " Cladoceres" and " Phyllopodes." The order 
* Regne Animal, vol. iv. p. 147 
f Histoire Naturelle des Crustaces, Suites a- Buffon, tom. i. Paris, 1834. 
