Oct., i894. ''PREFORMATION OR NEW FORMATION:' 293 



remains a large residuum, which can be explained only by the trans- 

 mission of a specific plasm from the parent to the sexual cell. In the 

 same tank of sea-water, surrounded by the same baneful and useful 

 circumstances, there may lie two fertilised egg-cells not differing 

 appreciably in appearance, in size, in chemical composition, or in 

 physical characters. Yet one of these produces a sea-hedgehog, 

 another a worm. The resemblances between the eggs of species of 

 the same genus may be still more remarkable, and the distinctive 

 characters may not appear till a late period in the course of the indi- 

 vidual development ; but the different specific characters do appear, 

 although there is nothing in the environment to cause them. The egg 

 of a barn-door fowl is as fully stamped with the character of its species 

 as is the adult animal. 



To explain the process of development, Hertwig believes that we 

 must postulate the existence of a material which contains germs or in- 

 cipia of a particulate character, and which possesses an extraordinarily 

 complicated structure corresponding to the marvellously minute and 

 complicated different ways in which it must react, as the growing 

 organism is built up by cell-multiplication. This material differs from 

 Weismann's conception of germ-plasm in many ways. First, it is not 

 built up of determinants and so forth into a complicated architecture. 

 Hertwig makes no supposition whatever as to the physical nature of 

 his specific material. Next, it by no means contains all the determining 

 causes of the organism. Many of these are due to external causes : 

 many more to the reaction between external causes and the material 

 itself. In this respect, it is true, there is no vital difference between 

 the two theories. Weismann at first attributed too much to the germ- 

 plasm and overlooked a number of ways in which the environment 

 plays a direct part in ontogeny. But recently he has reviewed and 

 accepted many external causes which he had hitherto passed by. 

 Both Weismann and Hertwig regard this specific material as con 

 taining the residual factors of development. Weismann may under- 

 state, or perhaps Hertwig overstate, the forces which have to be 

 allowed for before the residuum is reached ; but both are agreed that 

 there is a necessary residuum for which a specific inherited material 

 must be assumed. We come now, however, to the great point in 

 which the two views are wide as the poles asunder. Weismann, as 

 everybody knows, attributes to the sexual cells, and to special regions 

 called germ-tracks, the exclusive possession of the germinal plasm, 

 making an exception only of a few cases of special and probably 

 secondary adaptations. In consequence, he draws a sharp distinction 

 between the cells which contain the plasm and the somatic cells. New 

 organisms arise only from cells containing germ-plasm, and the somatic 

 cells, when they become specialised, lose the power of reproducing 

 the species as they contain, not germ-plasm, but a simpler derivative 

 of it. Hertwig, on the other hand, totally denies this sharp distinc- 

 tion. All the cells in the body receive an equal dower of the specific 



