354 'i"HE GERM-PLASM 



in the case of this particular character of the pigeon. The 

 frequent appearance of bars in crosses of different races of 

 pigeons indicates, on the contrary, that most individuals still 

 contain a number of these • bar "-determinants. We may, 

 however, conclude with regard to the occurrence of stripes like 

 those of the zebra on horses and asses, that the infrequency with 

 which reversion occurs, even in the case of crosses, is probably 

 due to the fact that the character in question has long ceased 

 to be present in a • latent ' condition in all individuals of both 

 species, and that the germ-plasm usually no longer contains 

 ' zebra '-determinants. 



We certainly cannot ascertain whether some few ancestral 

 determinants may not nevertheless still be present occasionally, 

 for even in crosses their cumulative effect might no longer be 

 apparent ; but general considerations compel us to assume that 

 even these sporadic old determinants must ultimately disappear. 

 They will be contained in the germ-plasm of a gradually de- 

 creasing number of individuals, and as these derive no benefit 

 from their presence, they will presumably become less and less 

 frequent. 



We must therefore take into consideration, on the one hand, 

 the dwindling specific or racial characters, which may be pres- 

 ent in a latent condition, though all of them need not by any 

 means necessarily occur in all individuals : and on the other, 

 the individual characters, which may exist in a latent condition 

 in a varying number of individual descendants. 



Tlie actual specific characters are. /ioii,'ever, transmitted to every 

 individual, though they also do not always become manifest, for 

 some regularly remain latent when another opposing group of 

 characters becomes apparent. I am here alluding to primary 

 and secondary sexual characters : but all characters — e\"en the 

 non-sexual ones due to dimorphism and polymorphism — come 

 under this category. I must now attempt to explain these 

 phenomena in accordance with my theory. 



In considering tliis problem, we must naturally begin with 

 the simplest case of sexual differentiation, in which the origi- 

 nallv monomorphic germ-cells become diiTerentiated into male 

 and female. The question then arises as to the origin of this 

 differentiation in the idioplasm, and how it has arisen phyleti- 

 cally. 



Let us take a definite example. The Volvocinece are lowly 



