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In his remarks "On the Origin of Insects," Sir John Lubbock says, "I feel great difficulty in conceiving by what natural process an insect with a suctorial mouth like that of a gnat or butterfly could be developed from a powerfully mandibulate type like the Orthoptera, or even from the Neuroptera." Is it not more difficult to account for the origin of the mouth-parts at all?
Thus if the rise of the Angiospermous vegetation on the ruins of the Mesozoic world is understood in the light of geological and climatic changes, and the consequent deploying of the insects, especially the suctorial insects, is a natural result, the simultaneous triumph of the birds is not unintelligible.
In the paddles of the gigantic extinct sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems thus to have become partially obscured.
The enormous mandibles of the adult Corydalus are too large for use and, as Walsh observed, are converted in the male into simple clasping organs. And to omit a number of instances, in the suctorial Hemiptera or bugs we have different grades of structure in the mouth-parts.
In the paddles of the extinct gigantic sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems to have been thus to a certain extent obscured. There is another and equally curious branch of the present subject; namely, the comparison not of the same part in different members of a class, but of the different parts or organs in the same individual.
In canis, for instance, the bull-dog and mastiff represent the ferocious sub-typical group; the waterdog is natatorial; we see the speed and length of muzzle of the suctorial group in the greyhound; and the bushy tail and gentle and serviceable character of the rasorial in the shepherd's dog and spaniel.
It seems that this habit was very widespread among the earlier Vertebrates; the larvae of many of the Ganoids and frogs have suctorial disks near the mouth. But apart from these peculiarities the Cyclostoma differ more widely from the fishes in other special features of their structure than the fishes do from man.
Next come the order of waders, who impart their quota to the perfection of the crow by giving it great powers of flight, and perfect facility in walking, such being among the chief attributes of the suctorial order.
In studying this over Manson reasoned that certain suctorial insects were the agencies through which blood was most commonly removed from the circulation and he ventured the guess that this change in the parasite that may be seen taking place on the slide under the microscope, normally takes place in the stomach of some insect that sucks man's blood.
Swainson calls them typical, sub-typical, natatorial, suctorial, and rasorial. Some of his illustrations of the principle are exceedingly interesting. He shews that the leading animal of a typical circle usually has a combination of properties concentrated in itself, without any of these preponderating remarkably over others.
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