Page:Popular Science Monthly Volume 14.djvu/222

210 whose guiding principle is an unreasoning attachment to what is established. Never, perhaps, was it shown more clearly than with reference to the present question that innovation may be retrograde—that a proposed change, if carried out, may involve a return to a lower stage of development. What is the very essence of all advance to a higher stage, of being, save differentiation? We see what was at first homogeneous, uniform in structure, become resolved into distinct tissues and members. We see functions which, in some rudimentary state, were jointly exercised by the whole body of an animal, gradually allotted out to special organs, and, during and in consequence of this very specialization, acquiring a far higher degree of perfection than they heretofore possessed. Look at the first rudimentary state—germ, seed, or ovum—of the plant or animal, and compare it with the mature organism to which it ultimately gives rise. What was one has become manifold; what was simple is now highly complex. The globule of albuminoid matter has developed into distinct members—sense-apparatus, organs respiratory, digestive, circulatory, locomotive, etc.—each of which has a separate task to fulfill, and is distinctly organized for that very purpose. It is no departure from our subject to remark that, though in the organic body one organ may, under certain circumstances, undertake the duties of another, such vicarious action involves grave peril to the organ concerned, and to the entire animal. Perhaps the world may yet find that the analogy between the individual and mankind holds good in this respect, and that a social congestion may follow from the movement we are examining.

To return: the increase of size which distinguishes the butterfly from the egg or the oak from the acorn, is a trifling feature compared with the accompanying differentiation—chemical, morphological, and functional—which has taken place.

If we pass from a consideration of the individual plant or animal to a survey of the entire organic realms, we find, as we advance from the humblest and meanest beings to the highest, merely a repetition of the same great fact. At the one extremity of the scale—if this expression may still be used—we find beings whose senses, such as they are, must be exercised by the whole external surface of the body, those more special functions which we know as sight, hearing, etc., being still identical with feeling. No distinct nervous system, still less definite nerve-centres, can be traced. Nor are there any organs specially devoted to the processes of respiration, circulation, digestion, etc. A common internal cavity takes the place, and, in a crude way, fulfills the duties of all these parts. Externally the same uniformity prevails; there are no limbs, no members exclusively constructed for locomotion in any of its modes, or for prehension. The animal moves by elongating and contracting its whole body, or by rolling over. In many of the lower forms of animal life the sexes are not separated, the functions of the male and the female being exercised by one and the same individual.