ENTOMOSTRACA 9 
of form in correspondence with diversity of function. The 
Isopoda, or equal-footed animals, besides being found both 
in fresh and salt water, have more decidedly than the 
Amphipoda extended their range to the dry land. The 
name was invented by Latreille in ignorance of the great 
number of species since investigated in which the feet are 
strikingly unlike and unequal. Nevertheless the name 
may stand, just as a rose remains a rose even when it is 
not rose-coloured. ‘T’o these three sub-orders some authors 
are disposed to add a fourth, the Tanaidea, while others, 
though agreeing to withdraw these animals from their old 
position among the Isopoda, would prefer to place them 
among the Amphipods. The need for the change in either 
direction has not yet been established. 
The Entomostraca, by their name, which literally means 
testaceous insects, bear witness to an era in classification 
when not only they but all other crustaceans were arranged 
among the Aptera or insects without wings. As the forms 
are multitudinous and very frequently microscopic, and as 
moreover crowds of the species have only been made known 
within recent years, it is not to be wondered at that the 
internal arrangement of this sub-class, like that of the 
preceding one, is still open on some points to discussion, 
although there is a fair amount of agreement as to the 
main lines of division. The method here followed dis- 
tinguishes three orders, the Branchiopéda, Ostracdda, and 
Copépéda. By Latreille the name Branchiopoda was ap- 
plied to the Entomostraca at large. It signifies branchial- 
footed, or animals in which the feet are in one way or 
another adapted to serve the purpose of respiration. This 
order is subdivided into four sub-orders. #. The Phyllo- 
cearida, literally leaf-shrimps, derive their name from the 
laminar or leaflike expansions with which their legs are 
provided. 2. The Phyllopdda, the leaf-footed ones, owe 
their name to the same characteristic, although by other 
features they are distinguished from the Phyllocarida. 
None of the Phyllopods are marine, although a few inhabit 
brackish water or strong brine. 3. The Cladocéra, which 
are so called from their branched antenne, occur chiefly 
