INTRODUCTORY REMARKS. 19 
Many structures of wasps have a peculiar con- 
formation, and, of course, in wasps only can these be 
thoroughly investigated. Conversely, we should 
look in vain in wasps for much that we find in other 
insects. If our idea, however, of insect structure in 
general is to be drawn from one insect, a wasp will 
serve as well as any other example. 
It might be said, fancifully perhaps, that in many 
respects an insect is like a vertebrate animal reversed. 
The student of human anatomy has his attention 
directed to each promimence on the outside of the 
bones as indicative of the strength of the muscle 
attached to it, and of the mechanical functions of 
the part. It is not outside, but inside the bones of 
insects that these indications are to be found, the 
same horny plates serving the purpose both of skin 
and bone. So again, while in Vertebrata the blood is 
brought from the tissues to the air in the lungs that 
it may be oxygenated, in insects, as we shall see, the 
air is brought to the tissues and to the blood lying 
loose in a series of membranous sinuses. And such 
illustrations might be multiplied. 
Again, fancifully, it might be said, taking an illus- 
tration from-the vegetable kingdom, that insects are 
endogenous, having their growth limited by their 
external investment, and their structure physio- 
logically prescribing the term of their existence. 
Subject to such restrictions, and within these limits, 
nothing more beautiful or perfect in adaptation can 
be conceived than these tiny organisms. They illus- 
trate perhaps the highest point to which organization 
can be carried on the endogenous plan. Larger size, 
capacity of growth, and longer duration of life, are 
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