1894. "PREFORMATION OR NEW FORMATION." 193 



ences, and through permutation can pass into other combinations. 

 As Hertwig puts it, the hereditary material contained in the egg and 

 spermatozoon can be made up only of those material particles which 

 are the bearers of cell properties. Every composite organism can 

 inherit its characters only in the form of cell characters. The 

 numerous indefinitely variable properties of animals and plants which 

 are expressed in the different form, structure, and function of their 

 different organs and tissues, and in the different relations between 

 them, are functions of cell complexes. They depend on the interaction 

 of many cells, and cannot have as their hereditary bearers material 

 particles in a cell. They are new structures which come into existence 

 only through the combination of cells with different individual 

 properties. 



Take as an example of the impossibility of determinants, the early 

 stages of the frog's development. 



In cleavage the nucleus plays the chief part, but to start this there 

 is needed not a special determinant, but the co-operation of all the 

 functions of the cell through assimilation of nutriment from the yolk. 

 The chromatin fibrils, which we can represent as independently 

 growing and dividing elements, have to be doubled in number. The 

 centrosome also must be independently doubled. All these processes 

 are the result of chemical and other changes depending on the 

 powers of the cell as an elementary organism, and extended to the 

 chromosomes as units of a lower order. The division of the nucleus 

 into two, four, eight, and so forth, gives the stimulus to the yolk- 

 mass to divide, and this exercises a strong influence upon the arrange- 

 ment of the cells and the direction of the planes of cleavage. But these 

 are not due to special determinants, for many of them are due to 

 the special properties of the yolk. Thus Hertwig himself has shown 

 that the direction of the planes of cleavage depends upon the 

 relations of the specific gravities of the various parts of the cell, 

 and that the unequal size of the cells and the unequal rate at which 

 they divide depend upon the separation of the protoplasm into 

 parts richer and poorer in yolk granules. No doubt the first three 

 cleavage planes often coincide with the future axes of the animal, and 

 this is laid hold of by Roux and Weismann as proof oi their view that 

 these planes separate cells containing material for the right and left 

 halves, and so forth. But these also Hertwig thinks he can show to 

 result not from specific determinants, but really to depend upon the 

 shape of the egg and the yolk distribution. Thus the shape of the 

 egg itself in many cases determines the necessary shape of the adult. 

 In the case of eggs, those with polar arrangement of yolk give rise to 

 polar segmentations, those with equal distribution of yolk give rise to 

 holoblastic division. In meroblastic eggs the richer or slighter 

 assembling of yolk, and therefore of specific gravity, is the determinant 

 of the special kind of embryo. In very many cases where the 



cleavages give the future axes, these are determined not by the 



o 



