August 26, 1898.] 



SCIENCE. 



247 



the appearance of Darwin's Origin of Species 

 may be roughly pointed out as follows : 



1. The claim by some thinkers of the in- 

 adequacy of Darwinism, as such, or Natural 

 Selection, to account for the rise of new 

 species, and the assignment of this factor to 

 what they believe to be its proper place 

 among the other factors of organic evolu- 

 tion. 



2. The renascence of Lamarckism under 

 the name of Neolamarckism, being La- 

 marckism in its modern form. This school 

 relies on the primaiy factors of evolution, 

 on changes in the environment, such as the 

 agency of the air, light, heat, cold, changes 

 In climate, use and disuse, isolation, and 

 parasitism, while it regards natural, sexual, 

 physiological, germinal and organic selec- 

 tion, competition or its absence, and the 

 inheritance of characters acquired during 

 the lifetime of the individual, as secondary 



-factors, calling into question the adequacy 

 of natural selection as an initial factor.- 



3. The rise of the ISTeodarwinian school. 

 While Darwin, soon after the publication 

 of the Origin of Species, somewhat changed 

 his views as to the adequacy of natural se- 

 lection, and favored changes in the sur- 

 roundings, food, etc., as causes of variation, 

 his successors, Wallace, Weismann and 

 others, believe in the ' all-sufGciency ' of 

 natural selection. Weismann also invokes 

 panmixia, or the absence of natural selec- 

 tion, as an important factor ; also amixia, 

 and denies the principle of inheritance of 

 acquired characters, or use-inheritance. 



4. A third school or sect has arisen un- 

 der the leadership of Weismann, who advo- 

 cates what is in its essence apparently a 

 revival of the exploded preformation, en- 

 casement or ' evolution ' theory of Swam- 

 merdam. Bonnet and Haller, as opposed to 

 the epigenetic evolutionism of Harvey, 

 Wolff, Baer and the majority of modern 

 embryologists. On the other hand, there 

 are some embryologists who appear to ac- 



cept the combined action of epigenesis and 

 evolution in development. 



5. Attention has been concentrated on 

 the study of variations and of their cause. 

 Opinion is divided as to whether variation is 

 fortuitous or definite and determined. Many 

 now take exception to the view, originally 

 held by Darwin, that variations are pur- 

 poseless and fortuitous, believing that they 

 are, for example, dependent on changes in 

 the environment which were determined in 

 early geological periods. For definite varia- 

 tions Eimer proposes the term orthogenesis. 

 Minute variations dependent on climatic 

 and other obscure and not readily appre- 

 ciable causes are now brought out clearly 

 by a system of varied and careful quantita- 

 tive measurements. 



6. More attention than formerly is given 

 to the study of dynamical evolution, or 

 kinetogenesis ; to the effect of external 

 stimuli, such as intermittent pressure, 

 mechanical stresses and tensions by the 

 muscles, etc., on hard parts. Originally 

 suggested by Herbert Spencer, that the 

 ultimate cause or mechanical genesis of the 

 segmentation of the vertebrate skeleton was 

 due to transverse strains, the segmentation 

 of the bodies of worms and arthropods, as 

 well as of vertebrates, has been discussed 

 by recent workers (Eider, Cope, Meyer, 

 Tornier, Hirsch and others.) Here should 

 be mentioned the work done in general 

 physiology, or morphogenesis, by Verworn, 

 Davenport and others. Also the discoveries 

 of Pasteur, and the application by Metschni- 

 koff and of Kowalevsky of phagocytosis to 

 the destruction and renewal of tissues dur- 

 ing metamorphosis, bear closely on evolu- 

 tional problems. 



7. A new field of research, founded by 

 Semper, Vilmorin and Plateau, and carried 

 on by DeVarigny, is that of experimental 

 evolution, involving the effects of artificial 

 changes of the medium, including tempera- 

 ture, food, variation in the volume of water 



