(4) Rudimentary Organs.–One of the special arguments commonly cited in favour of the evolution theory is based on the frequent occurrence of rudimentary structures in organisms. As examples we may mention the following: Pythons and boas possesses vestiges of hind legs and of a pelvis separated from the vertebral column.–The slow-worm is without external limbs, and yet possesses the shoulder-girdle and the pelvis, as well as a slightly developed breast-bone.–The ostrich has merely stunted wing-bones, while the nearly extinct kiwi (apteryx) of New Zealand has only extremely small stumps of wings, which are clothed with hair-like feathers.–The gigantic birds of New Zealand which became extinct in past ages were entirely wingless.–Well worthy of note, also are the rudimentary organs of the whale (Cetacea), since of the hind limbs only a few minute bones remain, and these are considered to be the pelvic bones, while the Greenland whale (Balœ;na mysticetus) also possesses thigh and leg bones. The bones of the fore-limbs are not movable independently of one another, being bound together by means of tendons–.Other remarkable vestigial structures are the teeth of the Arctic right whale, which never penetrate the gums and are reabsorbed before birth, the upper teeth of the ox, the milk teeth and the eyes of the mole. The deep sea fish, like the Barathronus, have instead of eyes "two golden metallic concave mirrors" (Chun).–Nor is man devoid of rudimentary organs. Wedersheim mentions no fewer than one hundred. But of these only a few are genuine. The vermiform appendix may serve as an example, though according to recent research it is not entirely functionless. Its length oscillates between 2 cm. and 23 cm., while its breadth and external form vary exceedingly. Probable reasons for its partially rudimentary character are, besides its extreme variability, especially two facts in particular: the length of the organ compared with that of the large intestine is as 1:10 in the embryo, and as 1:20 in the adult; secondly, in 32 per cent of all cases among adults of over twenty years of age the appendix is found to be closed.
Do such rudimentary organs furnish us with an acceptable proof for the theory of evolution?–It is to be admitted that in many instances the organs were formerly in a more perfect condition, so as to perform their typical functions–e.g., the eyes of the mole as organs of sight; and the limbs of the kiwi as means of locomotion for running or even for flying. Hence those individuals which now possesses rudimentary organs are descended from ancestors which were in possession of these same organs in a less degenerated condition. But it cannot be ascertained from the structures whether those ancestors were of another kind than their offspring. The vermiform appendix in man is fully explained by supposing it to have had in antediluvian man a more perfect function of secretion, or even of digestion. Until the palæontological records furnish us with evidence we can only conclude from the occurrence of rudimentary structures that in former ages the whale possessed better developed limbs, that the moles had better eyes, the kiwi wings, etc. In short, rudimentary organs per se do not prove more than that structures may dwindle away by disuse.
Haeckel's endeavour to invalidate the teleological argument has no foundation in fact. In many cases the function of rudimentary organs has been discovered–e.g., the rudimentary teeth of the whale are probably of use in the growth of the jaw; the breast-bone of the slow-worm as a protection of the chest. But even in instances in which we have not succeeded in discovering the function of such structures, it must not be forgotten that degeneration may be eminently teleological in furnishing material for other organs whose functions become more important. Moreover, as long as rudimentary organs remain, they may become, under altered circumstances, the starting-point for an appropriately modified reorganization. It is indeed difficult to see how "dysteleology", as Haeckel calls it, follows from the fact that an organ adapted to specified means of livelihood disappears, probably in order to strengthen other organs when those means of livelihood are changed; and, until the contrary is proved, we may assume that we have to deal with instances of teleological adaptation and correlation, as has already been demonstrated in many cases–e.g., in the development of amphibians.
