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hypothesis, to escape admitting the independent origins of closely similar forms. It may be that they are both more frequent and more important than is generally thought.
That closely similar structures may arise without a genetic relationship has been lately well urged by Mr. Ray Lankester.1 He has brought this notion forward even as regards the bones of the skull in osseous fishes and in mammals. He has done this on the ground that the probable common ancestor of mammals and of osseous fishes was a vertebrate animal of so low a type that it could not be supposed to have possessed a skull differentiated into distinct bony elements-even if it was bony at all. If the ancestral cranium was thus undifferentiated, then the cranial bones must have had an independent origin in each class, and in this case we have the most strikingly harmonious and parallel results from independent actions. For the bones of the skull in an osseous fish are so closely conformed to those of a mammal, that "both types of skull exhibit many bones in common," though "in each type some of these bones acquire special arrangements and very different magnitudes.” 2 And no investigator of homologies doubts that a considerable number of the bones which form the skull of any osseous fish are certainly homologous with the cranial bones of man. The occipital, the parietal, and frontal, the bones which surround the internal ear, the vomer, the premaxilla, and the quadrate bones, may be given as examples. Now, if such close relations of homology can be brought about independently of any but the most remote
1 See Ann. and Mag. of Nat. Hist., July 1870, p. 37.
2 Professor Huxley's Lectures on the Elements of Comp. Anat. p. 184.
genetic affinity, it would be rash to affirm dogmatically that there is any impossibility in the independent origin of such forms as centetes and solenodon, or of genetically distinct batrachians, as similar to each other as are some of the frogs of South America and of Europe. At the same time, such phenomena must at present be considered as very improbable, from the action of ancestral habit, as before stated.
We have seen, then, that the geographical distribution of animals presents difficulties, though not insuperable ones, for the Darwinian hypothesis. If, however, other reasons against it seem to have any weight-if, especially, there is reason to believe that geological time has not been sufficient for it, then it will be well to bear in mind the facts here enumerated. These facts, however, are not opposed to the doctrine of evolution; and if it could be established that closely similar forms had really arisen in complete independence one of the other, they would rather tend to strengthen and to support that theory.
Animals made-up of parts mutually related in various ways.-What homology is. Its various kinds.-Serial homology.-Lateral homology.— Vertical homology.—Mr. Herbert Spencer's explanations.—An internal power necessary, as shown by facts of comparative anatomy.-Of teratology.-M. St. Hilaire.-Professor Burt Wilder.-Foot-wings.-Facts of pathology.—Mr. James Paget.—Dr. William Budd.—The existence of such an internal power of individual development diminishes the improbability of an analogous law of specific origination.
THAT concrete whole which is spoken of as "an individual” (such, e.g., as a bird or a lobster) is formed of a more or less complex aggregation of parts which are actually (from whatever cause or causes) grouped together in a harmonious interdependency, and which have a multitude of complex relations amongst themselves.
The mind detects a certain number of these relations as it contemplates the various component parts of an individual in one or other direction-as it follows up different lines of thought. These perceived relations, though subjective, as relations, have nevertheless an objective foundation as real parts, or conditions of parts, of real wholes; they are, therefore, true relations, such, e.g., as those between the right and left hand, between the hand and the foot, &c.
The component parts of each concrete whole have also a relation of resemblance to the parts of other concrete wholes, whether of the same or of different kinds, as the resemblance between the hands of two men, or that between the hand of a man and the fore-paw of a cat.
Now, it is here contended that the relationships borne one to another by various component parts, imply the existence of some innate, internal condition, conveniently spoken of as a power or tendency, which is quite as mysterious as is any innate condition, power, or tendency resulting in the orderly evolution of successive specific manifestations. These relationships, as also this developmental power, will doubtless, in a certain sense, be somewhat further explained as science advances. But the result will be merely a shifting of the inexplicability a point backwards, by the intercalation of another step between the action of the internal condition or power and its external result. In the meantime, even if by "Natural Selection" we could eliminate the puzzles of the "origin of species," yet other phenomena, not less remarkable (namely, those noticed in this chapter), would still remain unexplained and inexplicable. It is not improbable that, could we arrive at the causes conditioning all the complex inter-relations between the several parts of one animal, we should at the same time obtain the key to unlock the secrets of specific origination.
It is desirable, then, to see what facts there are in animal organization which point to innate conditions (powers and tendencies) as yet unexplained, and upon which the theory of "Natural Selection" is unable to throw any explanatory light.
The facts to be considered are the phenomena of “homo
logy," and especially of serial, bilateral, and vertical homology.
The word "homology" indicates such a relation between two parts that they may be said in some sense to be "the same," or at least "of similar nature." This similarity, however, does not relate to the use to which parts are put, but only to their relative position with regard to other parts, or to their mode of origin. There are many kinds of homology,1 but it is only necessary to consider the three kinds above enumerated.
WING-BONES OF PTERODACTYLE, BAT, AND BIRD.
The term "homologous" may be applied to parts in two individual animals of different kinds, or to different parts of the same individual. Thus "the right and left hands," or "joints of the backbone," or "the teeth of the two jaws," are homologous parts of the same individual. But the arm of man, the foreleg of the horse, the paddle of the whale, and the wing of the bat and of the bird, are all
1 For an enumeration of the more obvious homological relationships see Ann. and Mag. of Nat. Hist. for August 1870, p. 118.