INTRODUCTION. ii 



germinal protoplasm retains its specific properties, 

 dividing in every reproduction into an ontogenetic por- 

 tion and a phylogenetic portion, which is reserved to 

 form the reproductive material of the mature offspring. 

 This reservation of the phylogenetic material I de- 

 scribed as the continuity of the germ-protoplasm. . . . 

 Encapsuled in the ontogenetic material the phyloge- 

 netic protoplasm is sheltered from external influences, 

 and retains its specific and embryonic characters. " In 

 other words, the reproductive cells are removed from 

 the influence of those stimuli which affect and effect 

 growth in the cells of the other parts of the body, so 

 that no character acquired by the rest of the body can 

 be inherited. The bearing of this theory on evolution 

 is thus stated by Weismann ; ^ "The origin of heredi- 

 tary individual variations cannot indeed be found in 

 the higher organisms, the metazoa and metaphyta, but 

 is to be sought for in the lowest, the unicellular." "The 

 formation of new species, which among the lower pro- 

 tozoa could be achieved without amphigony (sexual 

 union), could only be attained by means of this process 

 in the metazoa and metaphyta. It was only in this 

 way that hereditary individual differences could arise 

 and persist." In other words, variation in organic 

 beings above the unicellular forms, has been and is, 

 introduced only by sexual reproduction. 



The conclusions of Weismann were derived prin- 

 cipally from embryologic research, and his disciples 

 have been chiefly recruited from embryologists. These 

 conclusions have been supported by extensive and ex- 

 haustive investigations, which have added greatly to 

 our knowledge of the subject. In order to account for 



\ Essays, ■^. zyd. For a complete account of Weismann's views, see The 

 Germ-Plasm, 1893. 



