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The evolution of the arthropods reaches its culminating point in the insect, and in particular in the hymenoptera, as that of the vertebrates in man.
In others defensive armour is chiefly developed, and we get the lines of the heavy sluggish shell-fish, the Molluscs and Brachiopods, and, by a later compromise between speed and armour, the more active tough-coated Arthropods.
So, while nature has frankly evolved in the direction of instinct in the arthropods, we observe in almost all the vertebrates the striving after rather than the expansion of intelligence. It is instinct still which forms the basis of their psychical activity; but intelligence is there, and would fain supersede it.
There can be no doubt that many of the Arthropods, a division of animals more ancient and even now more prevalent than the Vertebrata, have undergone more phylogenetic modification" a beautiful phrase "than even the most modified of vertebrated animals. Simple forms like the lobsters display a primitive structure parallel with that of the fishes.
Hallowell in a company for which he is doing chemical research work. We are hatching eggs, out of the shell, so to speak. Also we are aging and rejuvenating arthropods and the like. So far we have declared no dividends. But we have hopes." She gave a hysterical sob of relief. "Then it's only business not the girl at all!" "Oh, yes, it's the girl, too," replied he. "She's an officer of the company.
There is excellent reason to believe that all animals, and especially such advanced forms as the vertebrates and the higher arthropods, have some power of mental development, some facility in devising new methods of action to meet new situations.
With more or less modification in detail, the embryo has been observed to pass through these successive evolutional stages in sundry Sponges, Coelenterates, Worms, Echinoderms, Tunicates, Arthropods, Mollusks, and Vertebrates; and there are valid reasons for the belief that all animals of higher organisation than the Protozoa, agree in the general character of the early stages of their individual evolution.
The highest group, the Cephalopods, "keep their heads," in the literal sense, and we shall find them advancing from form to form until, in the octopus of a later age, they discard the ancestral shell, and become the aristocrats of the Mollusc kingdom. The last and most important line that led upward from the chaos of Archaean worms is that of the Arthropods.
Probably arthropods and vertebrates were threatened with it too. They escaped, however, and to this fortunate circumstance is due the expansion of the highest forms of life. In two directions, in fact, we see the impulse of life to movement getting the upper hand again. The fishes exchanged their ganoid breast-plate for scales.
Mobility and suppleness were sought for, and also through many experimental attempts, and not without a tendency to excess of substance and brute force at the start variety of movements. But this quest itself took place in divergent directions. A glance at the nervous system of the arthropods and that of the vertebrates shows us the difference.
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