ANATOMY AND PHYSIOLOGY. 69 
aids to respiration. And so its respiratory organs 
are less perfect than those of creatures which are 
below it im the scale. Our own structure may point 
another illustration. A perfect vertebra, such as 
many fish possess, would be terribly in our way, with 
the anterior spinous process sticking out in front. 
And our perfect hands and feet would sadly interfere 
with the perfect adaptation of the seal and porpoise 
to their several spheres of existence. 
So, in speaking of anything being imperfect, it 
must be understood that this term cannot be applied 
absolutely and unreservedly concerning any animal 
structure. Everything in creation is perfect for its 
purpose. But the structure of each part is always 
adapted, subordinated, to the necessities of the 
animal. Each organ is always made as good as it is 
wanted, but no better; for a more elaborate structure 
is more easily deranged, and, in the absence of means 
of repair, soon becomes worse than useless. Complex 
arrangements are not employed where the end can 
be gained by simpler means. The life of most perfect 
insects is of very limited duration—the wasp is no 
exception to this general law—and is for a very 
definite object. So no more stores are laid in than 
are enough to carry the ship into port after her short 
voyage. ‘There are no spare spars, no materials for 
executing repairs; indeed, an injury to a perfect 
insect is irreparable. Everything is made on the 
simplest plan and in the way least likely to get out 
of repair. The cornea—in the instance of the com- 
pound eye now before us—is made to do the duty of 
the lens also. The moveable iris, with its muscles 
and blood-vessels, as seen in our own eyes, is replaced 
