212 COMPARATIVE ZOOLOGY. 
scapular and pelvic arches; the humerus and femur; car- 
pus and tarsus; the right and left sides of most animals; 
the dorsal and anal fins of Fishes; the arms of Man, the 
fore - legs of a Horse, the paddles of a Whale, the wings 
of a bird, the front flippers of a Turtle, and the pectoral 
fins of a Fish; the proboscis of a Moth, and the jaws of a 
Beetle; the shell of a Snail, and both valves of a Clam; 
the follicles of Invertebrates, and the compact liver of 
Vertebrates."* The wings of the Bird, Flying Squirrel, 
and Bat are hardly homologous, since the wing of the first 
is developed from the fore-limb only; that of the Squir- 
rel is an extension of the skin between the fore and hind 
limbs; while in the Bat the skin stretches between the 
fingers, and then down the side to the tail. The legs of 
a Lobster and Lizard; the wings of a butterfly and Bird; 
the gills of a Fish, and the lungs of other Vertebrates, are 
analogous. The air-bladder of a Fish is homologous with 
a lung, and analogous to the air-chambers of the Nautilus. 
The wings of Birds and Bats are both homologous and 
analogous; as likewise the contractile protoplasm of the 
Ameeba, and the muscular tissue of the Vertebrate. 
In the midst of the great variety of form and structure 
in the animal world, a certain harmony reigns. Not only 
are different species so related as to suggest a descent 
from the same ancestor, but the parts of any one organ- 
ism are so closely connected and mutually dependent, that 
the character of one must receive its stamp from the char- 
acters of all the rest. Thus, from a single tooth it may be 
inferred that the animal had a skeleton and spinal cord, 
and that it was a carnivorous hot-blooded Mammal.  Cer- 
tain structures always co-exist. Animals with two occipi- 
tal condyles, and non-nucleated blood - corpuscles, suckle 
their young, @.¢. they are Mammals. All Ruminant 
hoofed beasts have horns and cloven-feet. If the hoofs 
are even, the horns are even, as in the Ox; if odd, as in 
