The science of life : fully illustrated in tone and line and including many diagrams

THE EVIDENCE FROM PLANT AND ANIMAL STRUCTURE

Ichthyosaur

Fig. 131. The structural plan of the vertebrate’s fore-limb is exemplified by that of man.

The general plan remains the same throughout the vertebrates, from amphibians up, though the details may be

altered.

In the Frog, the two bones of the lower arm are fused.

In the Ichthyosaur, they are extremely

shortened, and extra rows of finger-bones are added. In the Dolphin, two of the fingers are elongated ; in the

Bat, four.

In the Pig, the thumb has vanished. In the Red Deer the second and JSifth fingers are on the way to

disappearance, and in the Camel only the third and fourth are left.

Even in limbs all serving the same function, the plan may be treated very differently and yet survive ; in the wing of a bird, the bones of wrist and palm are fused into one solid mass, and only three tiny fingers are retained ; the bat enlarges all the fingers except the first; while pterodactyls, the extinct flying reptiles, enlarged only the “little” finger ; or again, the flippers of some among the ichthyosaurs, though at first sight very like those of a whale, achieved their paddle-like shape by a new kind of variation on the original plan; they broadened themselves by adding to the original number of fingers until these numbered seven or even eight. If all higher vertebrates, from Amphibia up, are descended from one common stock with a fivefingered hand, all these curious details are illuminatingly sane ; if otherwise, they are incomprehensible (Fig. 132).

In precisely the same way, the jaws and mouth-parts of all insects conform to a single plan—the piercing, blood-sucking tube of the mosquito, the butterfly’s coiled miniature trunk for sipping nectar, the house-fly’s

licking proboscis with its expanded lobes, the stag-beetle’s formidable weapons of attack, the ant’s chewing apparatus—all can be reduced to a simple plan such as is most clearly seen in a grasshopper or cockroach, with an upper lip, one pair of strong mandibles, and two pairs of weaker maxillz, the second pair united to make a single lower lip (Fig. 133). Once more, if all insects are blood-relations, with bodies basically similar but specialized in divers ways to suit their diverse habits, the common plan of their jaw parts is easy to understand ; if they are all separate creations, then only the supposition of a monstrous pedantry in creation seems to afford a glimmer of elucidation.

Examples could be multiplied almost ad infinitum—the appendages of lobsters, crabs, and other crustaceans ; the teeth of mammals; the skull or the brain through the whole vertebrate series—all tell the same story. ;

A handful of different flowers gathered in a country walk would suffice for demonstration, if looked at searchingly with the

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