220 
LIFE, IN ITS INTERMEDIATE FORMS. 
would furnish a most interesting and instructive lesson in 
physiology. 
The broacl plates which expand like a fan at the tail of 
the Prawns and Lobsters, form their great resource for 
swift and sudden locomotion. The common Lobster is 
said to be able to dart back by this means thirty feet, with 
the fleetuess of a bird on the wing ; and when we think 
of this feat, we must not forget the great density and 
resistance of such a medium as water, in which it is 
accomplished. The existence of these plates, and the 
great development of the abdomen which carries them, 
distinguish these from the proper Crabs, which have 
no terminal plates, and in which the abdomen is re- 
duced to a thin flap bent under the body and pressed 
close to it, except when it is forced out of place by 
the spawn, which the females deposit between it and the 
thorax. 
Some of the Crabs have the power of swimming, but 
it is by a very different mechanism from that of the Lob- 
sters; and it affords us one of the many examples which 
the naturalist is constantly meeting with, of the infinite 
resources of the wisdom of God in creation. In the com- 
mon eatable Crab ( Cancer pagui'us), with the exception of 
the foremost pair of limbs, which are expanded into power- 
ful grasping claws, all the feet are terminated by a short 
sharp-pointed toe. But we have some species common on 
our shores (Portunus, cf-c.), in which the hindmost legs have 
the last joint dilated into a broad, thin, oval plate, which 
being fringed, as are also the other joints, with stiff hairs, 
constitute oars, and being worked in a peculiar manner, 
row the animals swiftly to and fro, at the surface or through 
