70 GENETICS 



of germplasm in sexual reproduction within a species, 

 and secondly, the mixture of two more remotely related 

 strains resulting in hybridization. In either case the 

 strain of germplasm undergoes a shake-up that may 

 result at least in new combinations of characters, if 

 not in the production of entirely new characters. This 

 recombination of characters in amphimixis and 

 hybridization will receive further attention in a later 

 chapter. 



The fact that successive parthenogenetic genera- 

 tions, in which amphimixis does not of course occur, 

 may show a larger degree of variability than sexually 

 produced generations, indicates that amphimixis in 

 itself is by no means sufficient to account for all kinds 

 of variations. 



It is conceivable that the external factors that act 

 upon the germplasm may be grouped into three classes : 

 first, external factors acting upon the somatoplasm 

 and then through the agency of the somatoplasm af- 

 fecting the germplasm ("somatic induction" of Detto 

 or "pangenesis" of Darwin) ; second, external factors 

 acting directly upon the germplasm and the somato- 

 plasm at the same time ("parallel induction" of 

 Detto) ; and third, external factors acting upon the 

 germplasm without necessarily at the same time hav- 

 ing any effect upon the somatoplasm. 



Many instances of direct influence of external fac- 

 tors upon germplasm are known in biological litera- 

 ture, and these have led to some of the misunderstand- 

 ings concerning the "interminable question" of the in- 

 heritance of acquired characters. Sitkowski fed the 

 caterpillars of the moth Tineola biselliella with an 



