422 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1912. 



called natural sciences, wliich owe to tliis method their most wonder- 

 ful advancement. It was very late, comparatively spealdng, when 

 the thought obtained that similar results might be expected in natural 

 history, and a few decades of tliis opinion have led to great results. 



I intend to-day to cover as far as possible, with many concrete 

 examples, the facts which I brought before you in abstract form. 

 We would, however, gain very Httle if I should attempt witliin the 

 time at my disposal to touch upon all the branches of natural history 

 to which experimentation has been apphed. I therefore prefer to 

 dwell upon only two leading questions viewed from the experimental 

 viewpoint, and shall consider these in considerable detail. These 

 are the old Lamarcldan and Darwinian slogans ''Adaptation and 

 inheritance." In their reactions, which we wish especially to em- 

 phasize, both of them become united in a single world-stirring prob- 

 lem. Pure description and comparison could not give them their 

 full meaning, they remained but empty terms, slogans, through 

 wliich one was supposed to be able to explain everything, but which 

 in truth possessed no explanation at all, and were therefore discred- 

 ited, especially tlirough the critical examination to wliich they were 

 subjected by the genial August Weismann. The reaction between 

 adaptation and inheritance, or, differently stated, the transmission 

 of characters acquired tlii'ough adaptation, the emphasizing of these 

 characters, and the evolutionary effect produced thereby upon the 

 parent stem of the organism, had scarcely any followers for a long 

 time. It required and wiU require many tedious and prolonged 

 experiments before that almost abandoned study wiU be revived in 

 improved form, stronger and better entitled to consideration. We 

 shall therefore, among all the problems of evolution, here confine 

 our attention to adaptation and inheritance, but we shall constantly 

 be in touch with that other large problem, that of reproduction. In 

 tliis we shall give equal consideration to asexual reproduction by 

 simple fission (Paramaecium) ^ or budding (worm Aeolosoma), the 

 unisexual reproduction by parthenogenetic eggs (lower crustaceans), 

 or close fcrtihzation (liigher plants), and even the bisexual reproduc- 

 tion through the union of ovum and spermatozoa of two distinct 

 indi\dduals, a male and a female (liigher animals). 



On account of the manifold adaptations of wliich we shall learn, 

 the foUo\ving problems of modern biology will be touched upon, 

 namely, Embryogenesis, or germ development; Regeneration, or 

 repeated growth (worm Lumbriculus) ; Involution or Concentration 

 (worm Aeolosoma); Transplantation, or grafting (salamander, chicken, 

 rabbit, guinea pig); Mendehan law (midwife toad); Intravitem 

 staining, or coloring of living tissues (moth Tineola) ; Immunity, or 



• The names of the organisms which furnish data for the problems of this lecture are added in parentheses 

 to make it easier to locate them in the proper place. 



