154 LIFE AND HER CHILDREN. 
here a creature much more alive to everything around 
him than the groping star-fish or the creeping worm, 
while the active little crab as he peers out from the 
seaweed, and scrambles across the shallow pools, or 
buries himself in an instant in the wet sand, shows 
a lightness and agility which we look for in vain in 
the sluggish snail or the slowly-grazing limpet. 
And when we learn that the prawn and the crab in 
the sea are formed on the same plan as the centipedes, 
spiders, and insects of the land, we see that we are 
on the road to even more intelligent and more active 
creatures, such as the busy bee and the thrifty ant. 
But how can this be, that the heavy armour-covered 
crab and lobster, which are called Crustacea from their 
hard crust-like shells, should belong to the same type 
as the delicate hovering butterfly, and the buzzing 
gnat ? Let us pause and master this, for till we 
have done so, we cannot understand the wonderful 
way in which the creatures of each group in this divi- 
sion have been adapted to the life they have to lead. 
In Fig. 55 we have four animals a prawn, a 
centipede, a spider, and a caterpillar together with 
the butterfly into which it turns. Now all these 
animals wear their skeleton, or the hard part of their 
bodies, not inside as we do with soft flesh growing 
over it, but outside ; so that if you grasp any of them 
when dead, the skin (as we should call it) will bend 
or crack like a piece of thin horn. Moreover, this 
hard outside skeleton is arranged more or less in 
rings with softer skin between them, as you may see 
in the centipede and caterpillar, and in the hind part 
of the prawn and butterfly ; and they are to be traced 
in many spiders, though as a rule they have disap- 
