I879-] 
in the Organic World . 
4i 
jointly, this disease would be induced earlier in life, and 
would occur not merely in the lower extremities, but in the 
regions of the trunk below the level of the heart. The in- 
creased adtion of the latter organ, further, could scarcely 
fail to bring on aneurism. 
If we then admit that gravitation tends to limit the size 
of organic beings, presenting difficulties which grow with 
their growth, we shall be in a position to explain certain 
general phenomena of the animal and vegetable kingdoms 
which have hitherto been for the most part accepted as 
ultimate fadts. It is a familiar observation that every sub- 
stance, living or lifeless, weighs less the denser the medium 
in which it is plunged, or, more accurately speaking, the 
nearer the specific gravity of such medium approaches its 
own. If we raise a stone which is lying under water, we 
find its weight increase suddenly the moment we have lifted 
it above the surface. This simple experiment may show us 
that a creature inhabiting the land, and having its body 
ordinarily immersed in air, experiences greater difficulty in 
supporting its own weight than would a being of equal size 
and formed of similar materials, but framed to live in the 
water. The former has to spend a greater proportion of its 
energies in fighting against gravitation than the latter. 
Again, a creature which passes a great portion of its time 
not merely immersed in air, but suspended in it, has a still 
harder struggle against gravitation than either of the two 
former, and will find its vital force still more severely taxed. 
Hence we might expert to find the inhabitants of the air, 
in the strictest sense of the term (i.e., Cheiroptera , birds, 
and winged insedts), small ; the inhabitants of the water 
largest ; whilst the dwellers on land — immersed, indeed, in 
air, but supported to a great extent by the firm ground — 
should occupy an intermediate position. 
This agrees substantially with what we find on an adtual 
examination of the animal kingdom. If we take the two 
leading sub-kingdoms, the Annulosa and the Vertebrata, 
each of which includes a vast number of aquatic, of terres- 
trial, and of aerial species, we find that in every case their 
largest-sized members are inhabitants of the waters. The 
first of these sub-kingdoms includes the inserts, the myria- 
pods, the spiders and their allies, and the crustaceans. But 
everyone knows that certain of the latter group, such as the 
crabs and lobsters, far surpass the remaining classes in 
magnitude. Who, for instance, ever found a beetle, a cock- 
roach, locust, scorpion, centipede, or spider weighing 5 lbs. ? 
Yet a crustacean of 15 to 20 lbs. is by no means un- 
exampled. 
