1894- ''PREFORMATION OR NEW FORMATION." 191 



theory, the part of the germ-plasm required to direct an individual 

 ontogeny gets broken up and distributed to the various cells of the 

 embryo by a series of heirs-unequal divisions. By this means the 

 cells of the soma come to contain only the determinants which can 

 produce cells of their own order. The exceptions are not numerous. 

 There is, first, the great exception by which unaltered germ-plasm is 

 passed along the germ-tracks to the place of origin of the sexual cells. 

 Next there are a few special cases of adaptation to the needs of 

 regeneration and bud formation in which a certain amount of reserve 

 nuclear matter is retained. Against this Hertwig asserts that all cell- 

 division is by heirs-equal division, and, therefore, every cell, in addition 

 to its patent characters, retains the power of producing on emergency 

 all the species-characters. He goes on such facts as these. In 

 single-celled organisms all cell-division obviously is heirs-equal 

 division. In the lower animals and plants, almost any cell, when 

 occasion demands, may become a sexual cell. Regeneration of lost 

 parts, and still more heteromorphosis, show that each cell is not 

 limited in its capacity to its predestined sphere of work, but can 

 reproduce totally distinct parts of the organism, and can reproduce 

 them in such a way that the specific characters are maintained. The 

 results of grafting, transplantation of tissue, and transfusion of 

 blood, show that cells beside their patent tissue-characters contain 

 latent species-characters, and that, generally speaking, the resem- 

 blance between sexual affinities and vegetative affinities shows that 

 tissue cells are as equally specific as sexual cells. 



Considerations Against the Doctrine of Determinants. 



With his doctrine of heirs-unequal division, Weismann has united 

 his theory of determinants in the germ-plasm of the fertilised egg-cell. 

 Each independently varying part of the adult is represented by 

 biophores united into a determinant. The various determinants are 

 arranged in the plasm or are endowed with such powers that they 

 come liberated at the proper time to enter into the cells to form the 

 determinate. Hertwig's criticism of this, and his arguments against 

 it, are strongly epigenetic. In the modern, as in the older, doctrines of 

 preformation, he sees the same confusion between sequence and 

 causation. If the ancestor of the whole chain of animal-life were an 

 amoeba, it would be an empty and meaningless phrase to say that the 

 amoeba contained in any real sense the material germ of all the 

 subsequent animals that arise from it. Similarly, although all the 

 cells of the body have their origin from the egg-cell, it is no necessary 

 consequence that the material germs of all subsequent tissues and 

 cells are contained in the egg-cell. The egg and the adult do not 

 form a closed chain of forces. Many other conditions must be 

 present. 



Every organic development depends, for instance, upon the 

 absorption and metamorphosis of nutritive materials. The cells grow 



