506 



SCIENCE. 



[N.S. Vol. XVI. No. 404. 



deficiency. The farm would enable iis to 

 work out life-histories, bring us face to 

 face with instinct, put it under control 

 so that we could handle it, photograph it, 

 analyze it, read its history, and extort from 

 it an answer to the question. Whence and 

 how came intelligence? 



It wotild enable us to extend the study of 

 development beyond the stages represented 

 in the egg and the embryo to those leading 

 up to mature age, and thus bring within 

 reach vast series of most important data 

 for the study of evolution. 



In such data we might expect to see to 

 what extent individual development re- 

 capitulates race development, and to get 

 important clues to the meaning of this so- 

 called biogenetic law. The whole meaning 

 of development and heredity is involved 

 in these phenomena of 'recapitulation.' 

 That the first step in recapitulation is the 

 germ-cell, we know. The fertilized germ, 

 or egg, passes through a series of form- 

 stages, leading through the morula, blas- 

 tula, gastrula, embryo, larva, etc. Whether 

 these stages epitomize the ancestral series 

 is a question very difficult to decide, and 

 opinion is much divided. This obscure but 

 fundamental problem of development can 

 probably never be solved by embryological 

 data alone. Paleontology throws much 

 light on the general question, but deals 

 entirely with non-living remains. If there 

 be recapitulation, it should certainly be 

 discoverable in post-embryonic stages, 

 where characteristic features are slowly 

 elaborated and brought to a completion in 

 detail quite beyond the possibilities in ear- 

 lier life. Strange to say, these later stages 

 have been but little studied in living forms, 

 museum morgues having been the chief 

 reliance. It is in these stages that recapitu- 

 lation may be actually seen as a life-pro- 

 cess, successive steps in evolution repeating 

 themselves with sufficient fullness to satisfy 

 the most skeptical. Such sequences are 



often manifest in the development of in- 

 stinctive behavior, and even in voice- 

 changes and food-instincts at certain life- 

 epochs corresponding seemingly to evolution 

 epochs. Remembering that the distant an- 

 cestors of land animals were undoubtedly 

 aquatic, the history of individual develop- 

 ment in amphibious forms of to-day be- 

 comes intelligible as an abbreviated and 

 variously modified record of race develop- 

 ment. Making all allowance for secondary 

 adaptive changes, it is nevertheless safe 

 to say that race evolution is sketched in 

 the development of the individual — 

 sketched not only in fundamental features 

 of structure, but also in the accompanying 

 physiological and psychological changes.- 



Reminiscences of aquatic life are seen 

 not only in land animals that return to the 

 water to deposit their eggs, but also in all 

 the higher animals, since they begin life 

 in the unicellular stage and require for 

 their first development to be bathed in 

 fluid. 



Sequence in color-patterns, so charac- 

 teristic of young animals of almost all spe- 

 cies, and especially so of birds, furnishes 

 innumerable illustrations of the biogenetic 

 law, and in many cases, where only two 

 extremes of the sequence are present, it is 

 possible by simple experiment to bridge 

 the gap, and thus to show that the two ex- 

 tremes are really two stages of a continuous 

 development. For example, in some wild 

 species of pigeons we find that the color- 

 pattern of the first pliunage succeeding 

 the down is so different from that of the 

 second (adult) plumage, as to appear, to 

 have no direct developmental relation to it. 

 By plticking one or more feathers from the 

 first plumage at different times before the 

 first molt, intermediate stages can be ob- 

 tained, showing precisely how the first pat- 

 tern can be progressively converted into 

 the second. Such experiments enable us 



