GENERAL CHARACTERS. 
9 
great majority being less than an inch long, and none 
exceeding thrice that length. Like all the productions 
of nature of diminished size, the number of indivi- 
duals of different species far exceeds that of the larger- 
sized Crustacea. With few exceptions, there is but little 
external difference of form between the opposite sexes ; 
the males, however, contrary to the ordinary rule in the 
Annulosa, being often larger than the females. There is 
also but little difference in form between the young and 
adult individuals of the several species, except where 
marked characters exist, such as the enlarged form of the 
hands, or spines on the different segments of the body, 
which increase in size as the animals become older. The 
species occur in temperate or high latitudes in greater 
proportion than in tropical climates. 
Thus it will be perceived that among the Amphipoda 
there is a considerable variety of form, some keeping 
closer to the typical idea of the Order, while others vary 
more or less considerably. It is therefore desirable, both 
for clearness of expression and in order to obtain a 
better knowledge of the whole, that we should arrange 
together those which more nearly assimilate to each other ; 
whereas others, which vary in a greater or less degree, 
should be grouped according to their respective details. 
In the works of Leach, Latreille, Milne-Edwards, 
Kroyer, Dana, Zaddach, Liljeborg, and Bruzelius, various 
modes of classification of these animals have been pro- 
posed. Based upon a consideration of these various ar- 
rangements, as well as upon the structure and respective 
habits of the different animals (resulting from a consider- 
able observation of their economy and modes of life), 
and having had the advantage of studying the types of 
Montagu, Leach, Phipps, M. -Edwards, and others, we 
have drawn up the following tabular distribution of the 
Order : — 
