422 EVOLUTION AND GENETICS 



do not know enough of inheritance to say that the blood stream 

 contains only certain things in connection with one character and 

 other things for its allelomorph. It is at least possible that the 

 same constituents are present in all cases, hence, no matter what 

 the character of a body, cells introduced into it might be expected 

 to avail themselves of the nourishment so provided without losing 

 their own integrity. It has been suggested also that albinism may 

 be due to the absence of a factor, and that a negative condition 

 in the soma could hardly be expected to exert control over the 

 germ cells. 



Neo-Lamarckian Theories. The opposition of Neo-Darwinian 

 evolutionists to the Lamarckian theory has l^ecn such as to con- 

 centrate attention upon the supposed integrity of the germ plasm. 

 It has come to l:)e a ver}^ commonly accepted principle that the 

 demonstrable continuity of the germ plasm through successive 

 generations is evidence that it is a thing apart from the soma, 

 influencing it but not influenced in turn. The soma is regarded 

 as a derivative of the germ plasm which develops anew in every 

 generation but fails to make any contribution to the heritage of 

 the species. 



The Fallacy of Germinal Continuity. In organisms which always 

 reproduce by sexual processes continuity of the germ plasm is 

 readily demonstrable. The germ cells produced by an individual 

 are obviously derived from the zygote which produced it, and in 

 turn contribute to the zygote from which the germ cells and 

 bodies of the next generation arise. In roundworms of the genus 

 Ascaris this continuity has been demonstrated with unusual 

 clarity, for after a few cleavages one cell of the segmenting zygote 

 is set aside as the parent of all germ cells while the rest develop 

 into the body of the worm. Continuity of this evident kind is 

 not often noted, however, and in some of the plants and lower 

 animals we find evidence of continuity of other tissues and even 

 of discontinuity of the germ plasm. Many plants can be developed 

 from fragments of somatic tissue. In such cases we may have 

 continuity of root, stem or leaf tissue from generation to generation. 

 Animals such as Hydra display a similar continuity and in the 

 flatworms Child has demonstrated the development of germ cells 

 from somatic tissues, in addition to the somatic continuity made 

 evident by the asexual reproduction of these worms (Fig. 210). 



The prevalence of sexual reproduction among the more famihar 



