THE MAILED WARRIORS OF THE SEA. 177 
the chief forms. The King-crab"' of the Moluccas, 
with his horseshoe carapace and spiked tail, repre- 
sents a whole race which flourished long before the 
coal-forests grew. The beautiful little fairy-shrimpsf 
of our ponds are another type whose feet are used as 
breathing-gills, while the tiny water-flea J and cypris 
of our ponds are true crustaceans, though they have 
two-valved shells like a scallop. 
The histories of these little beings are as yet not 
much known, and in truth it is impossible to follow 
out all the strange vagaries of the Crustacea with- 
out making them a life study. Even when we have 
exhausted those which live independent lives, there 
remains a whole mass of parasites which fix them- 
selves on the backs and in the gills of fishes, and 
even under the tails of their distant relations the 
crabs and lobsters. 
Thus we find that these "insects of the sea" 
have spread everywhere where there is water, and 
have even found their way on to the land. Yet 
they are scarcely likely ever to make much way on 
dry ground, for we have seen that they have always 
a lingering tendency to breathe water, and therefore 
they are at a disadvantage among the myriads of 
insects fitted for the air. Meanwhile, though we 
may know more of the habits of the spider and ant, 
than of the crabs and the barnacles which hide from 
us in the ocean, yet those who love to study compli- 
cated family history will find no class in the animal 
kingdom with such an interesting and involved 
genealogy as that of the Crustacea or crust-covered 
animals. 
* Limulus. t Branchipus. Daphne. 
