ORTHOGENESIS 301 



to environmental action — such are the supplementary 

 factors in species-forming. 



Besides this general theory of phylogenesis, Eimer 

 drew from the results of his personal observations 

 certain conclusions which he calls ''laws of organic 

 growth." Those laws, of varying importance and 

 value, are intended to supplement his theory of ortho- 

 genesis and to determine the line followed by the evo- 

 lution of living things. He states among other things, 

 that development may come to a standstill or retro- 

 gress; that the same characters may develop identi- 

 cally in individuals not otherwise related ; that colour- 

 ation in the most different animals, molluscs, birds, 

 reptiles, mammals, and certain insects, appears first 

 in longitudinal bands; those bands afterwards break 

 up in spots, which blend in cross bands, and finally, 

 by spreading more and more, produce a uniform 

 colour, etc., etc. 



Many of the statements made by Eimer are appar- 

 ently founded on facts, but his theory is not convinc- 

 ing. His laws are mere statements of facts the cause 

 of which is not determined. The reasons why char- 

 acters in their development follow an upward or 

 downward direction without deviating from a definite 

 line, remains very obscure. Eimer declares that he 

 does not attribute to the organism any mysterious 

 property in order to explain its tendency to develop 

 along one definite line, and that environment is the 



