INTRODUCTION. XIX 
Pe 
the sternum. In the Macrura, it also forms part of 
the sternum, but the separation is distinguishable by 
a free and movable articulation. In the Sessile-eyed 
Crustacea, the coxa is more laterally situated, and very 
firmly attached, without being fused to the segment of 
the body. With few exceptions, it is developed into 
a broad and scale-like joint, and is so large in the 
Stegocephalide that it covers the greater part of the 
animal. The object of this development is evidently to 
cover and protect the branchial appendages, when situated 
beneath the pereion. These scale-like cox have been 
considered as parts of the segments of the body of the 
animal to which the legs belong, and are described under 
the name of epimera, or side-pieces, by Professor Milne 
Edwards. 
There is a peculiar tendency in the Amphipoda for the 
joints of the legs to be produced in a scale-like form. 
Besides the coxe, the dasis, or second joint of the three 
posterior pairs of pereiopoda, are almost always so de- 
veloped. In Orchestia, the males in some species have the 
carpus and posterior pair of pereiopoda enlarged ; in Podo- 
cerus and Cerapus, the two auterior pairs have the basis 
so produced; but in Sulcator this predisposition appears 
to reach the culminating point, where it is apparent in 
almost every joint of the appendages of the head and 
body. 
The next division of the animal is that which we deno- 
minate the pleon. It consists of seven segments, as in 
each of the former divisions, and carries three kinds of 
appendages. The segments generally resemble those of 
the pereion, and, like them, carry on each side squamiform 
coxze, which Professor Milne Edwards has again mistaken 
for epimera, or side-pieces, belonging to each respective 
segment. ‘These are, both in the Amphipoda and Isopoda, 
b2 
