Agassiz's _Essay on Classification_, which was published in October, 1857, was the last manifesto issued before the _Origin of Species_ by the party which stood out for fixity of species, the last polemic which made De Maillet, Lamarck, and the _Vestiges_ its targets. It is an eloquent but inconsiderate defence of an extreme position. According to Agassiz every branch, class, order, family, genus, and species represents a distinct creative thought; every mark of affinity, every appearance of adaptation to surroundings, has been expressly designed. Extinction and replacement of species are due to the direct intervention of the Creator; pterodactyls are prophetic types of birds, and indicate that divine wisdom had foreseen the possibility of an advance in the organisation of animals which was not immediately practicable; the mallard and scaup duck occur on both sides of the Atlantic because they were simultaneously but separately created in Europe and North America; the teeth of the whale, which never cut the gum, are the result of obedience to a certain uniformity of fundamental structure. Explanations like these removed no difficulties and suggested no inquiries. In the hot debates which ensued the _Essay on Classification_ was rarely mentioned. [32] _Cross and Self-Fertilisation of Plants_, chap. xi. Darwin could exhaust the inquiry. "The veil of secrecy," he goes on, "is as yet far from lifted." [33] Cuvier did not himself use the word _palæontology_, which first came in about 1830. In the same way Buffon writes on the history of animals, not on _zoology_, and on the theory of the earth, not on _geology_. [34] This anecdote has also been related in a rather different form. [35] The same process of "embryonic fission" occurs in other animals also, one of which is a mammal (Praopus). [36] Linnæus (Fund. Bot. § 134, and Sponsalia Plantarum) gives it as above; Harvey has "Ex ovo omnia"; "ovum esse primordium commune omnibus animalibus," etc. [37] Harvey need not have gone outside the writings of Aristotle to get the substance of his generalisation. He would have found there that the chief task of both plants and animals is propagation, either by seeds, or eggs, which Aristotle believed to be equivalent to seeds (_Hist. anim._, VIII., i.; _De anim. gen._, I., iv.; I., xxiii.). Aristotle excepted the "imperfect animals," such as insects, and the seedless plants, concerning both of which his knowledge was misty and inaccurate; there is no indication that Harvey was better informed.