52 Heredity. 



that they shall be of inconceivable minuteness, and that 

 nature furnishes no analogy for attributing to such small 

 particles the vital properties which we kno\v only in 

 bodies which are comparatively gigantic. It is also 

 urged that the gemmules must be endowed with entirely 

 imaginary and wonderfully specialized elective affinities, 

 in virtue of which each develops only at the proper time 

 and place. In order to account for the manner in which 

 the characteristics of each parent are mingled in the 

 child we must regard each individual as the product of a 

 struggle for existence among the gemmules, resulting in 

 the selection and development of the fittest. The for- 

 mation of several individuals asexually by budding from 

 a parent stock demands that the gemmules themselves 

 must be capable of multiplication, and that they must 

 have the power to transmit their properties to their off- 

 spring. To explain alternation of generations we must 

 suppose that the embryo receives several complete sets 

 of gemmules, which are not duplicates, and it is almost 

 impossible to follow out, in thought, the complicated re- 

 lations which must exist between the gemmules of the 

 egg-embryo of such an organism as a Siphonophore. 



These and similar objections may be fairly urged, 

 and while their great weight is obvious, we must not 

 attach undue importance to them, for they do not show 

 that the hypothesis conflicts with any known law or ob- 

 served fact, and the great drafts made upon the imagina- 

 tion should not, alone, prevent its provisional accept- 

 ance so long as we have no simple explanation of the 

 phenomena, for difficulty in imagining the details of an 

 hypothesis is a purely subjective matter, which varies 

 with the age and with the individual. 



