292 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



13. " Mutations of Waagen," 2 1869, or continuous variations in time. 



14. "Mutations of De Vries." 1 



15. "Definite variations," Osborn (1891). 

 "Phylogenic variations," Osborn (1893). 

 "Rectigradations,"' Osborn (1905). 



16. Potential homologies [non-Homoplasy], Osborn (1902). 



The recent distinction of Johannsen between the "genotype," or genetype 

 (Osborn) as an assemblage of genes and the phenotype is also the distinction 

 between heredity, as here conceived, and ontogeny. 



Ontogenic, phenotypic, or somatic expressions of heredity may be roughly 



classified as follows 



f Recapitulations of ancestral history. 

 Ancestral predispositions. 

 Ancestral correlations. 



f Repetitions of type. -{ Regressive fluctuations, or deviations around a mean. 



Regressions. 

 Reversions. 

 Ancestral dominants and recessives. 



Classification of f Germinal modifications. 



t h e somatic-^ Slow progress or alter- £ J opewive fluctuations, or deviations around a mean 

 expressions of] ations of type. "ons of Waagen. 



heredity. 



j 



Rectigradations of Osborn. 

 [ Phylogenic degeneration, development. 



Sudden alterations of f Saltations, sports, 

 type. I Neogenic characters or neomorphs. 



The "potential homology" of Osborn (1902) is one of the most mysterious 

 manifestations of the forces of heredity, which predisposes descendants of a 

 similar stock, however remote, to give rise to similar new characters through 

 heredity. This principle, which the author considers to be absolutely demon- 

 strated in the case of the evolution of the teeth and of the horns of the titano- 



* 



theres, has also been less positively observed by other zoologists as well as by 

 botanists. Recent investigators of the mutation phenomena of De Vries have 

 remarked the tendency of plants to give rise to similar new "mutants" in widely 

 separated localities. It is noteworthy that this principle was clearly recognized 

 by Darwin in his Origin of Species: 



. . . The principle formerly alluded to under the term of analogical variation has probably in 

 these cases often come into play; that is, the members of the same class, although only distantly aiiie , 

 have inherited so much in common in their constitution, that they are apt to vary under simi 

 exciting causes in a similar manner; and this would obviously aid in the acquirement through na . 

 selection of parts or organs, strikingly like each other, independently of their direct inhentance ir 

 a common progenitor. 2 



Considering the ontogenic expressions of heredity as they appear in palae- 

 ontological series, we may repeat our statement above that blastic evolution is 

 the most mysterious and also the most elusive of phenomena so far as are con- 

 cerned the laws which govern the orderly origin and appearance of new characters. 



We note the following significant questions for investigation : 



1 "Mutations" of Waagen and "Mutations" of De Vries or [andl "Rectigradations" of Osborn. 

 Science, N. S., vol. XXXIII, No. 844, Mar. 3, 1911, p. 328. 



* Origin of Species, vol. II, p. 221. Edition of 1909, D. Appleton & Co., 2 vols, in one. 



