Heredity and Environment 



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 197-205. 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- 



FIG. 37. X-RAY PICTURE OF RIGHT AND LEFT HANDS EACH WITH Six 

 FINGERS (polydactyly) caused by splitting of the little fingers at an early 

 stage. (From Journal of Heredity.) 



