ENTOMOSTEACA 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. To 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 Branchiopoda, Ostracoda, and 

 Copepoda. By Latreille the name Branchiopoda was ap- 

 plied to the Entomostraca at large. It signifies branchial7 

 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. 1. The Phyllp- 

 carida, literally leaf-shrimps, derive their name from the 

 laminar or leaflike expansions with which their legs are 

 provided. 2. The Phyllopoda, 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 Cladocera, which 

 are so called from their branched antennas, occur chiefly 



