2 
AMPPIIPODA. 
carapace covering the upper portion of the segments of 
the body, consequently these segments are themselves 
made dorsally perfect ; second, the gnathopoda, which, 
in the Macroura, constitute the two outer pairs of mouth- 
organs, become prehensile instruments, increasing the 
number of legs to seven pairs ; and, third, the tail, or 
caudal apparatus, consists of four segments instead of 
two. 
In the Amphipoda, on the other hand, the various seg- 
ments are nearly equally developed throughout, whilst, 
from being generally compressed at the sides, or cylin- 
drical in form, the animals of this order are easily dis- 
tinguished from the Isopods, which are, for the most 
part, broad and flattened in shape.* 
2 
* Hence, to a certain degree, the Amphipoda constitute a group parallel 
in their own division with the Macroura amongst the Decapoda , whilst the 
Isopoda form an analogous group to the broad and flattened Brachyura, 
the Caprellce offering a kind of parallelism with Squilla and its allies. 
