IV WEISMANN ON THE GROWTH OF THE GERM- PLASM 85 



again only a very small fragment can remain unchanged 

 when the germ-cell develops into an animal, therefore, even 

 within a single individual, a quite enormous growth of germ- 

 plasm from this fragment must occur. In every individual, 

 as a rule, thousands of germ-cells are produced. It is thus 

 not too much to say that the growth of the germ-plasm in 

 the Egyptian Ibis or the crocodile in those 4000 years must 

 have been utterly immeasurable. In the plants and animals, 

 however, which inhabit equally the Alps and the Polar Eegions, 

 we have examples of species which have continued unchanged 

 for much longer periods, namely, since the ice age, in which, 

 therefore, the growth of germ -plasm must have been much 

 greater. 



" Since, nevertheless, the molecular structure of the germ- 

 plasm has remained exactly the same, it must be very hard 

 to modify, and there is little prospect that the slight 

 temporary differences in nutrition which will of course 

 liappen to the germ-cells as well as to every other part of the 

 organism, will bring about any change, however small, in its 

 molecular structure. Its growth will proceed now faster now 

 more slowly, but its structure will be affected thereby all the 

 less that tliese influences are mostly of an alternating 

 character, and act now in one direction now in another." 



The hereditary individual differences Weismann infers 

 must therefore have another root — they are to be derived 

 from sexual reproduction.-^ 



Against the above exposition, which reproduces once more 

 Weismann's whole theory of the continuity of the germ- 

 plasm, I must repeat that I cannot conceive how the germ- 

 plasm grows, grows to an enormous extent, without being 

 influenced by the conditions of nutrition, by the composition 

 of the body. What is the cause of its growth, and why is it 

 sometimes faster sometimes slower ? 



^ Die Bedentung der sexuellen Fortpjlanzung^ etc., p. 27 et seq. 



