302 LECTURES ON BIOLOGY 



carrier and transmitter of the heritable qualities, and this won- 

 derful substance must therefore contain a corresponding ' rudi- 

 ment ' (Anlage) for each heritable characteristic of the parents. 

 Without this assumption the very elaborate processes in the 

 course of mitosis, which manifestly aim only at the most 

 accurate distribution of the chromosome substance, are without 

 any reason ; and only with it can we obtain a teleological con- 

 ception of these mysterious phenomena. 



Investigations of parthenogenesis and ephebogenesis further 

 showed incontestably that the nucleus of the mature ovum, as 

 well as the head-nucleus of the spermatozoon, must contain 

 the complete ' rudiments ' (Anlagen) of at least one complete 

 individual. Fertilized egg-cells would, therefore, virtually con- 

 tain the ' rudiments ' of at least two perfect organisms, one of 

 paternal, the other of maternal descent. We may therefore 

 assume that during the embryonic development a struggle for 

 predominance takes place between paternal and maternal ' pairs 

 of characters,' and that upon its result depends the question 

 whether afterwards the child shall exhibit a corresponding quality 

 of its father or its mother. The ' rudiment ' of the characteristic 

 of the defeated part is of course also contained in its cells, but 

 it remains latent. 



Upon the more delicate structure of the * nuclear loops,' and 

 the distribution and arrangements of the various * primary con- 

 stituents ' (Anlagen) in them, we have not yet expressed an 

 opinion, as the observations made so far afford no foundation 

 for satisfactory conclusion. 



Several years ago Weismann constructed an ingenious theory 

 of heredity in which he undertakes to analyse the organization 

 of the chromosome into the minutest details ; but though he 

 seeks to defend his theory with the utmost sagacity, and though 

 he marshals numerous reasons in support, his arguments enter 

 far too much into the region of pure hypothesis and find but 

 little corroboration in the facts of observation. We may there- 

 fore content ourselves with a brief sketch of his theory of 

 germ-plasm. 



If we examine greatly magnified ' nuclear-loops ' of different 

 animals at various stages of development, we see that the 

 apparently uniform ribbons are formed of a large number of 



