1006.] on The Physical Basis of Life. 415 



They lead us, however, to a riddle which I leave to my readers to 

 solve as they will. We are driven to believe that in the material 

 make-up of any race there are several kinds of living matter whicli 

 cannot be changed the one into the other, and of which some will 

 mix, others will not or cannot mix. These materials, bricks, as it 

 were, in the building, are transmitted from generation to generation 

 by the agency of the germ cells, which therefore are hetei-ogeneous 

 structures.* Now, the doctrine of the direct transmission of the 

 various living substances employed in the make-up of tlie individual 

 lands us in this difficulty. The fertilised Qg^ has all the material 

 necessary for the make-up, therefore it can, and does, develop into an 

 adult. The generative cells also possess amongst them all the 

 necessary material. Therefore, amongst the earlier generations of cells 

 produced by the growth and division of the fertilised ovum, that cell 

 or those cells which will form the generative organs must contain all 

 the substances. But direct experiment contradicts this conclusion. 

 Possibly in the very first cleavage, certainly in the second cleavage 

 of the Qgg, there is a distribution of material amongst the two or four 

 cells such that each one lacks something in the general make-up, and 

 therefore can, and will, grow only to an imperfect monster if isolated. 

 But one of those four incomplete cells will give rise, amongst other 

 things, to the generative organs, each cell of which, in the first 

 instance, is complete. Therefore, as we may " neither confound 

 the persons nor divide the substance," we seem to be in a region of 

 incomprehensibles. 



" Just as that normal truth to type," says Bateson, " which we 

 call heredity is in its simplest elements only an expression of that 

 qualitative symmetry characteristic of all non-differentiating cell 

 divisions, so is genetic variation the expression o"^ a qualitative 

 asymmetry beginning in gameto-genesis [the genesis, that is, of the 

 germ cells]. Variation is a novel cell division. . . . What is the 

 cause of variation ? " Cross breeding — that is, the union of unlike 

 germ cells — may modify the character units. So, too, apparently may 

 the long-continued absence of cross breeding. It has been noticed in 

 the cycles of a pure strain of paramoecium that the periods of depressed 

 vitality are also periods when the directive force of heredity is 

 weakened. The individuals of successive generations show great 

 departures from the normal type, and monsters are of frequent 

 occurrence. With the lowered rate of growth, the lowered " vitality," 

 as we call it, for want of a more precise word, there is associated a 

 lowered degree of fixity of type. [W. B. H.] 



* The beginnings of the science of their architecture are to be found in the 

 last report of Mr. Bateson and Mr. Punnett to the Committee of the Royal 

 Society on Evolution. 



