OTHER THEORIES OF SPECIES-FORMING. 



environmental forces may produce a gradual or sudden change 

 according to circumstances. The combustion of food liberates the 

 moving force, environment guides it as it does the planets. 



" 'When once the persistent type is broken up, old latent forces 

 may be liberated and types buried in the dim past reappear. This, 

 called atavism, is a concentration of ancestral forces reverberating 

 echoes from varieties long since passed away, exhibiting them- 

 selves when from some cause, for instance crossing, present forces 

 are in a state of antagonism, division, perturbation, or weakness. 

 These echoes, if collected by crossing and selection, produce com- 

 binations of superlative importance and value.' " 



7 Plate, L., "Uber die Bedeutung," etc., p. 220. 



8 See Koken, Ernst, "Palseontologie und Descendenzlehre," 1902. 

 Koken (Professor of Geology and Palaeontology in the University 



Orthogenetic f Tubingen) is very explicit in the statements of his 

 variation in belief that the palaeontological records prove the exist- 

 paleontology, ence o f orthogenetic variation and hence evolution. 

 "Das Darwin'sche Prinzip der Selektion ist nicht das einzige, das. 

 in Betracht kommt und es scheint nicht das wichtigste zu sein. 

 Vielfach vermissen wir in der palseontologischen Geschichte den 

 Hinweis auf ein Eingreifen des Kampfes urns Dasein und anderer- 

 seits heben sich Richtungen der Entwickelung herans. welche nicht 

 in Beziehung zu einem Nutzen stehen, in einigen Fallen zu einer 

 Schadigung der socialen Bedingungen fiihren." 



9 For an account of the facts of one such case, see Kellogg, "Is-. 

 There Determinate Variation," Science, N. S., Vol. XXIV, pp. 621- 

 628, 1906. In this paper the gradual but obvious change from. 



A case of ap- one dominant type of colour-pattern to another in 

 parent determi- the leaf-eating beetle Diabrotica soror (on the campus, 

 nate variation, o f Stanford University, California) during the last, 

 ten years, is shown by statistical variation studies. It is shown 

 that such change is not explicable on a basis of intra-specific 

 selection, nor can it be interpreted as a direct ontogenic reaction 

 in each succeeding generation to changing climatic conditions. The 

 case is believed to be an example of definitive orthogenetic: 

 variation. 



Certain examples of presumable determinate variation have been, 

 recorded by Henslow ("The Origin of Species," Natural Science, 

 p. 259, 1894). "In 1847, Prof. J. Buckman sowed, seed of wild 

 parsnip in the garden of the Agricultural College, at Cirencester. 

 The seedlings began to vary, but in the same way, though in differ- 

 ent degrees. By selecting seed from the best rooted plants, the 

 acquired 'somatic' characters of .an enlarged root, glabrous leaves, 

 etc., became fixed and hereditary; and 'The Student,' as he calledi 



