MODERN SCIENCE. 143 



verifiable facts, whilst his treatise on " Sexual Selection," 

 which expounds the celebrated " Theory of Courtship," 

 explains a very important element of organic evolutionism. 

 We may mention also that his " Effects of Cross and Self- 

 Fertilisation in the Vegetable World" (1876) called 

 attention to the now well-known Knight's law " Cross- 

 fertilisation produces finer and healthier offspring, while 

 continuous self-fertilisation tends to final extinction " ; and 

 to Sprengel's beautiful work, " Fertilisation in Flowers," 

 which had been lying in the dust of libraries ever since 1789, 

 despite its intense interest and worth. That more than eight 

 hundred works on the same subject should have appeared 

 since Darwin drew attention to Sprengel may give an idea 

 of the germinal force that lay in his labours. 



It is bare justice to state that Mr. Alfred R. WALLACE was 

 working independently in the same direction as Darwin 

 himself, and that he arrived at similar conclusions about 

 the same time, after four years' work in Brazilian forests, and 

 eight years' explorations in the Malay Archipelago. The 

 writings of this fervent servant of science* are worthy of 

 Darwin himself. 



Since Darwin's death, Darwinism may be said to present 

 three groups of inquirers : I. the Wallace-Haeckel group, who 

 are orthodox Darwinians ; II. the Herbert Spencer group, 

 who are rather inclined to Lamarckianism ; III. the Weismann- 

 Romanes group, who explain variation as due to external 

 influences, and among these to sexual reproduction mainly. 

 Weismann thinks his theory of the continuity of the germ- 

 plasm is the key to the problem. For, the egg-cell (if we 

 may use the common term) will be affected by the sperm- 

 cell which unites with it, and the offspring receiving the 

 variation inherent in the sperm-cell, is itself different from 

 both parents, and will carry its own variation, by the trans- 

 mission of its germ-plasm, to its immediate descendant, whose 

 nature will in like manner be affected by the process just in- 

 dicated and repeated by its progenitor. This theory would 

 clear up the mystery of the cause of variation. Before it is 



* " Travels on the Amazons and the Rio Negro," " Tropical Nature," 

 "Geographical Distribution of Animals." 



