Page:Popular Science Monthly Volume 33.djvu/489

Rh in ancestral types, they are of no use in the types possessing them; and as being rudimentary they are of necessity imperfect. Moreover besides being injurious as taxing nutrition to no purpose, they are almost certainly in some cases injurious by being in the way. Then, beyond the argument from rudimentary organs, there is the argument from make-shift organs, which form a large class. We have a conspicuous case in the swimming organ of the seal, formed by the apposition of the two hind limbs—an organ manifestly inferior to one specially shaped for its function, and one which during early stages of the changes which have produced it must have been inefficient. But the untruth of the assumption is best shown by comparing a given organ in a low type of creature with the same organ in a high type. The alimentary canal, for example, in very inferior creatures is a simple tube, substantially alike from end to end, and having throughout all its parts the same function. But in a superior creature this tube is differentiated into œsophagus, stomach (or stomachs), small and large intestines with their various appended glands pouring in secretions. Now if this last form of alimentary canal is to be regarded as a perfect organ, or something like it, what shall we say of the original form; and what shall we say of all those forms lying between the two? The vascular system, again, furnishes a clear instance. The primitive heart is nothing but a dilatation of the great blood-vessel—a pulsatile sac. But a mammal has a four-chambered heart with valves, by the aid of which the blood is propelled through the lungs for aëration, and throughout the system at large for general purposes. If this four-chambered heart is a perfect organ, what is the primitive heart, and what are the hearts possessed by all the multitudinous creatures below the higher vertebrata? Manifestly the process of evolution implies a continual replacing of creatures having inferior organs, by creatures having superior organs; leaving such of the inferior as can survive to occupy inferior spheres of life. This is not only so throughout the whole animal creation up to Man himself, but it is so within the limits of the human race. Both the brains and the lower limbs of various inferior races are ineffective organs, compared with those of superior races. Nay, even in the highest type of Man we have obvious imperfections. The structure of the groin is imperfect: the frequent ruptures which result from it would have been prevented by closure of the inguinal rings during foetal life after they had performed their office. That all-important organ the vertebral column, too, is as yet but incompletely adapted to the upright posture. Only while the vigor is considerable can there be maintained, without appreciable effort, those muscular contractions which produce the sigmoid flexure, and bring the lumbar portion into such a position that