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SESSILE-EYED CRUSTACEA. 
Order AMPHIPODA * 
This name was given by Latreille to the present 
order f of Crustacea on account of the animals contained 
in it having both swimming and walking legs, and to 
distinguish it from the order Isopoda, in which the legs 
are adapted for walking only. 
The Amphipods exhibit the characters of the great 
class of which they are a part, more typically perhaps 
than any other Crustacea. In the higher orders, the 
head, from its great development, encroaches upon the 
body, and in the lower orders, the body encroaches upon 
the head. The type J of a class, order, or indeed any 
other group, is to be found in its centre, and not at 
either extremity of the series. 
The Amphipoda are formed upon the Macroural type, 
from the normal condition of which they differ in the 
three following important particulars : first, there is no 
* Derived from the Greek both ; trofog, feet. 
+ It must be borne in mind that, for the considerations set forth in the 
Introduction, the order Lsemodipoda, proposed by Latreille for Caprella and 
its allies, has been rejected — that group being regarded as an aberrant 
division of the Amphipoda. 
J The following definition of a type is given by Professor Whewell, as the 
92 nd aphorism concerning ideas, in his ‘ 1 Philosophy of the Inductive 
Sciences:” — “Natural groups are best described, not by any definition 
which marks their boundaries, but by a type which marks their centre. The 
type of any natural group is an example which possesses, in a marked degree, 
all the leading characters of the class.” 
B 
K [ Oiv At l\ 
' \. 6: V- 1 m. 
