206 CLOSE OF THE PRE-EVOLUTIONARY PERIOD 



and he has been forced to modify in some respects the rigour 

 of his doctrine. But he still holds fast to the main thesis of 

 transcendentalism the absolute unity of plan of all animals, 

 vertebrate and invertebrate alike, 1 the gradual perfecting of 

 organisation from monad to man, the repetition in the 

 embryogeny of the higher animals of the " zoogeny " of the 

 lower. 



He recognised, however, that the idea of a simple scale 

 of beings is only an abstraction, and that the true repetition 

 is of organs rather than of organisms. He was willing even 

 to admit, at least in the later pages of his memoir, that there 

 might be not one animal series but several parallel series, as 

 had been suggested by Isidore Geoffroy St Hilaire (p. 749). 

 In general, his views are now less dogmatic than they were 

 in his earlier writings, but they are not for all that changed 

 in any essential. For, in summing up his main results, he 

 writes, " The whole animal kingdom can in some measure be 

 regarded ideally as a single animal, which, in the course of 

 formation and metamorphosis in its diverse manifestations, 

 here and there arrests its own development, and thus 

 determines at each point of interruption, by the very state it 

 has reached, the distinctive characters of the phyla, the 

 classes, families, genera, and species" (p. S33). 2 



To settle the dispute pending between two of its most 

 illustrious members, the Academy proposed in 1853, as the 

 subject of one of its prizes, " the positive determination of 

 the resemblances and differences in the comparative develop- 

 ment of Vertebrates and Invertebrates." A memoir was 

 presented the next year by Lereboullet 3 which met with 

 the approval cf the Academy in so far as its statements of 

 fact were concerned, but seemed to them to require amplifica- 



1 The inversion of the organs shown by Vertebrates as compared 

 with Invertebrates is due to the reversed position of the embryo 

 relatively to the yolk ! (pp. 821-6). 



; It is wo! tli while recording that Serrcs enunciated a "law of 

 symmetry" according to which the embryo is formed by the union of its 

 two symmetrical halves a law which recalls the "concrescence theory" 

 of His and some modern cmbryologists. 



: " Kmbnolngic comparee du Brochet, de la Perche, et de 1'Ecrc- 

 visse," Ann. Set. nat. (4), i., p. 237, 1854 ; ii., p. 39, 1854. M<i. 

 Savons etrangers^ xvii. 



