

64 Evolution 



the web first appeared) thought that the flying exertions 

 of the early bat would strengthen and extend the web 

 during its individual life (a9 a limb is improved by 

 exercise), and that the improvement gained by the 

 individual would be inherited by its progeny. If this 

 went on for many generations the full evolution of the 

 bat's patagium would be easy to understand. 



Until recent decades this was held by all evolutionists, 

 but Weismann and his school are wholly opposed to it. 

 Weismann's theory of germ-plasm — a theory that only 

 the germinal matter passes from parent to offspring — is 

 quite inconsistent with it, and it is claimed that experi- 

 ment decides against it. There is, according to this 

 school, no inheritance whatever of characters or improve- 

 ments acquired by the individual in his single life-time.* 

 According to Weismann, the variation one finds in off- 

 spring of the same species or parents is due to different 

 tendencies in the germ-plasm, or differences in the 

 nutrition of parts of the germ, etc. There is a struggle 

 for food going on between the particles that compose 

 the germ, and as one or other prevails it will tend to 

 develop or modify an organ in a special way in the adult 

 body. So the variations arise by chance, so to say, or 

 without purpose. If they are useful, the individuals are 

 preserved, and the germ-plasm goes on developing them 

 — say the webby fore-limb of the bat — in succeeding 



* This is now the prevailing opinion amongst zoologists. 

 Francis Darwin and Sir W. Turner are among the few op- 

 ponents of distinction in England. In Germany, however, a 

 number of eminent zoologists (Eimer, Haeckel, Hering, 

 Zehnder, Plate, Kassowitz, etc.) still maintain the Lamarckian 

 position, and it has many supporters in France, America, and 

 elsewhere. On the other hand, Weismann says that there are 

 only two authorities in Europe (Professors J. A. Thomson 

 and Emery) who admit his whole system, and this is hardly 

 true of Professor Thomson, 



