568 THE HISTORY OF BIOLOGY 



Among the positive proofs he includes a number of experiments carried out 

 by the physiologist Brown-Sequard, who believed that by interfering with 

 the nervous system in guinea-pigs he had induced epilepsy in their young; 

 these experiments, however, have been found by other investigators either 

 to have miscarried or to have been misinterpreted. Giard has better success 

 when, in a controversy with Weismann, he declares that the secondary fac- 

 tors alone cannot explain the origin of the forms of life; he points out a 

 number of phenomena that cannot be explained by selection alone. On the 

 other hand, he does not deny the existence of selection, as already mentioned 

 above; he only considers its importance to be "secondary." 



0. Hertwig against natural selection 

 A FAR more severe judgment than that of Giard and several other Lamarckists 

 — for example, the famous American paleontologist E. D. Cope (1840- 

 57) — is passed upon the theory of selection by Oscar Hertwig, who de- 

 voted the latter part of his life particularly to attacking the common belief 

 in it. In fact, in his great work of 1916, referred to above. Das Werden der 

 Organismen, he finally settles his account with that theory and at the same 

 time gives a summary of the natural philosophy which he had produced in 

 the course of a long life that had been unusually rich in experience. Being 

 mainly a cytologist, Hertwig attaches decisive importance to the cell and 

 its structure as the groundwork for all speculation upon evolution. To him 

 the cell is the elementary organism and he vehemently sets his face against 

 all theories of biophores, plastidules, and such lower vital entities. Every 

 form of life has its peculiar cell-structure : there are in nature as many ' ' species 

 cells" as species; it is the character of the species cell that causes every form 

 of life to be what it is and produces descendants of the same kind. Evolution 

 is regulated in each separate case by the character of the species cell, and 

 those phenomena that coincide therewith are described as the " biogenetical 

 law of cause," which precludes the possibility of any such biogenetical prin- 

 ciple as that which Haeckel conceived; in its embryonic development a mam- 

 mal certainly does not pass through a series of stages identical with the 

 lower animals, but rather the egg of every mammal species is just as fully 

 specialized as the animal itself, and similarly with the embryonic stages. The 

 tgg contains within itself all the characters of the organism as rudiments; 

 Hertwig, following Nageli, terms the bearer of the rudiment within the 

 cell "idioplasma," but he is generally content to speak of the rudiments of 

 the species cell. Towards the question of heredity he adopts a decidedly 

 morphological attitude and insists that the material basis of the relative 

 phenomena must be observed and explored, thereby opposing Johannsen's 

 physiological view of the phenomena of heredity. He most emphatically 

 maintains the heredity of acquired characters — that is to say, the metab- 

 olistic influence of environment upon the hereditary dispositions. In support 



