H2 Heredity and Environment 



symmetry and pattern of the egg and of the adult animal which 

 is derived from it (see p. 190). These characters are of such a 

 general sort that they may not be recognized as phenomena of 

 inheritance at all, and yet they form the background and frame- 

 work for all the other characters. They do not come equally 

 from the egg and sperm, and they do not undergo segregation in 

 the formation of the gametes, but are apparently derived from the 

 egg cytoplasm. Among characters of this sort are the normal 

 and inverse symmetry of snails, and of many other animals, 

 including man, which are referred to on pages 191-195. Such 

 characters are undoubtedly inherited, though they differ from 

 other characters not only in the fact that they are transmitted 

 through the egg only, but also because they are of the same kind 

 in the egg and in the developed organism ; they are in a measure 

 preformed in the egg; they are differentiated characters carried 

 over from a previous generation rather than inheritance factors. 

 These egg characters probably appeared in the course of oogenesis 

 under the influence of paternal as well as of maternal factors ; 

 if so this is a case of Mendelian inheritance in the previous 

 generation or what may be called "Pre-inheritance." Similar 

 phenomena have been described by McCracken and by Toyama 

 in silk-worms where several egg characters seem to be non- 

 Mendelian, but Toyama has shown that they are in reality Men- 

 delian in the previous generation, this also being a case of pre- 

 inheritance. 



Somewhat similarly it has been found by Correns, Baur, and 

 Shull that the leaf colors of certain plants are not inherited in 

 Mendelian fashion, but the chromoplasts, which produce the chro- 

 matophores (chloroplasts), are transmitted from one generation 

 to the next in the cytoplasm of the egg cell and only rarely through 

 the male sex cell. If chromoplasts are integral parts of a plant 

 and undergo differentiation or development this may be a case of 

 pre-inheritance; if they are symbiotic organisms it is an instance 

 of the inclusion of foreign bodies in the cytoplasm and not in- 

 heritance at all. 



