Language such as that we have quoted is, in fact, so preposterous, so utterly incompatible with anything but absolute ignorance of some of the best established facts, that we should have passed it over in silence had it not appeared to afford some clue to M. Flourens' unhesitating, _a priori_, repudiation of all forms of the doctrine of the progressive modification of living beings. He whose mind remains uninfluenced by an acquaintance with the phaenomena of development, must indeed lack one of the chief motives towards the endeavour to trace a genetic relation between the different existing forms of life. Those who are ignorant of Geology, find no difficulty in believing that the world was made as it is; and the shepherd, untutored in history, sees no reason to regard the green mounds which indicate the site of a Roman camp, as aught but part and parcel of the primaeval hill-side. So M. Flourens, who believes that embryos are formed "tout d'un coup," naturally finds no difficulty in conceiving that species came into existence in the same way. FOOTNOTES: [65] "Die Radiolarien: eine Monographie," p. 231. [66] Space will not allow us to give Professor Koelliker's arguments in detail; our readers will find a full and accurate version of them in the _Reader_ for August 13th and 20th, 1864. [67] If, on the contrary, we follow the analogy of the more complex forms of Agamogenesis, such as that exhibited by some _Trematoda_ and by the _Aphides_, the Hyaena must produce, asexually, a brood of asexual Dogs, from which other sexless Dogs must proceed. At the end of a certain number of terms of the series, the Dogs would acquire sexes and generate young; but these young would be, not Dogs, but Hyaenas. In fact, we have _demonstrated_, in Agamogenetic phaenomena, that inevitable recurrence to the original type, which is _asserted_ to be true of variations in general, by Mr. Darwin's opponents; and which, if the assertion could be changed into a demonstration, would, in fact, be fatal to his hypothesis. XIV. ON DESCARTES' "DISCOURSE TOUCHING THE METHOD OF USING ONE'S REASON RIGHTLY AND OF SEEKING SCIENTIFIC TRUTH."