LIMITED LIFE OF ENDOGENS. 181 
we have all read so much, would be a mere 
pigmy to the huge cask which would fit over 
our accumulated barrels. If we were to make a 
section of all these 
barrels completely 
across, and look at 
the cut extremities, 
we should see, as is 
¥ DIAGRAM OF AN DIAGRAM OF AN 
represented in the EXOGEN. ENDOGEN. 
adjoining cut, the almost exact resemblance of 
the cross-cut stem of an Exogen; and doing 
the same with the barrel, into the interior of 
which we had thrust a number of hollow tubes 
or rods, we have something of the resemblance 
of an Endogen. The drawing will, we trust, 
make this very easy of comprehension. 
Even if we suppose the outer case of the 
Endogen to be in some measure able to expand, 
yet it is evident there would be a limit even to 
that, and beyond this it could not stretch. Yet 
while it is true theoretically that a limit to 
the life of Endogens must or may exist, it is 
also true that we are unable to fix it in the 
present state of our knowledge on this subject. 
Therefore our wisest course is to say, that 
