In the ratio of the knowledge of the reason of the coinci dences of animal structures—in other words, as those coinci • Diseours sur les Itholutions de la Surface du Globe, 4to, 1826, p. 50.
dences become " correlations "—is our faith in the soundness of the conclusions deduced from the application of such rational law of correlations ; and with the certainty of such application is associated a greater facility of its application. A knowledge of the physiological conditions governing the relations of the contents of the cavities of bones to the flight and other modes of locomotion in birds both enabled the writer to infer from one fragment of a skeleton that it belonged to a terrestrial bird deprived of the power of flight, and to predict that such a bird, but of less rapid course than the ostrich, would ultimately be found in New Zealand.* This principle, however—those modes of thought—which Cuvier affirmed to have guided him in his interpretation of fossil remains, and which he believed to be a true clue in such researches, were repudiated or contested by some of his contem poraries.
Geoffroy St. Hilaire denied the existence of a design in the construction of any part of an organized body ; he protested against the deduction of a purpose from the contemplation of such structures as the valves of the veins or the converging lens of the eye.
Beyond the co-existence of such a form of flood-gate with such a course of the fluid, or of such a course of light with such a converging medium, Geoffroy affirmed that thought, at least his mode of thinking, could not sanely, or ought not to go.
The present is not the place for even the briefest summary of the arguments which have been adduced by teleologists, and antiteleologists from Democritus and Plato down to Comte and WhewelL The writer would merely remark, that in the degree in which the reasoning faculty is developed on this planet and is exercised by our species, it appears to be a more healthy and normal condition of such faculty,—certainly one which has been productive of most accession to truths, as exemplified in the mental workings of an Aristotle, a Galen, a Harvey, and a Cuvier,—to admit the instinctive impression of a design or purpose in such structures as the valves of the vascular system and the dioptric mechanism of the eye. In regard to the few intellects,—they have ever been a small and unfruitful minority,—who do not receive that impression and will not admit the validity or existence of final causes in physiology, the writer has elsewhere expressed his belief that such intel lects are not the higher and more normal examples, but rather manifest some, perhaps congenital, defect of mind, allied or analogous to " colour-blindness " through defect of the optic nerve, or the inaudibleness of notes above a certain pitch through defect of the acoustic nerve.
The truth of a physiological knowledge of the condition of a correlated structure, and of the application of that know ledge to paheontology, is not affected by instances adduced from that much more extensive series of coincident structures of which the physiological condition is not yet known. Nor
is the power of the application of the physiologically interpreted correlation the less certain because the merely empirically re cognized coincidences have failed to restore, with the same certainty and to the same extent, an extinct form of animal.
Certain coincidences of form and structure in animal bodies are determined by observation. By the exercise of a higher faculty the reason, or a reason, of these coincidences is dis covered, and they become correlations ; in other words, it is known not only that they do exist, but how they are related to each other. In the case of coincidences of the latter kind, or of " correlations " properly so called, the mind infers with greater certainty and confidence, in their application to a fossil, than in the case of coincidences which are held to be constant only because so many instances of them have been observed.
Because the application of the latter kind of coincidences is limited to the actual amount of observation at the period of such application, and because mistakes have been made through a miscalculation of the value of such amount, it has been argued that a rational law of the correlation of animal forms is inapplicable to the determination of a whole from a part ;* and it has not only been asserted that the results of such determination are unsound, but that the philosopher who believed himself guided by such law deceived himself and misconceived his own mental processes ! t But the true state of the case is, that the non-applicability of Cuvier's law in certain cases is not due to its non-existence, but to the limited extent to which it is understood.
The consciousness of that limitation led the enunciator of the law to call the attention of expressly to the extent to which it could then be applied, as, for instance, to the determination of the class, but not the order ; or of the order, but not the family or genus, etc. ; and to caution them also as to the extent of the cases in which, the coincidences being only known empirically, he consequently enjoins the necessity of further observation, and of caution in their induc tion. envier expresses, however, his belief that such coin cidences must have a sufficient cause, and that cause once discovered, they then become correlations and enter into the category of the higher law. Future comparative anatomists will have that great consummation in view, and its result, doubtlessly, will be the vindication of the full value of the law in the interpretation of fossil remains as defined by the illus trious founder of paleontology.