FOSSILS-THEIR NATURE AND INTERPRETATION. 95 



of the adult ; and the prefix phyl thus phylephebic to denote 

 the characteristics of adulthood in racial evolution, assuming, 

 as these authors do, that races in evolution have their charac- 

 teristic stages corresponding to the stages of development of 

 the individual. There can be no doubt that in the growth of 

 the organism there is this general law of progressive change 

 of form and structure with its embryonic, adolescent, adult, 

 and senile stages, more or less distinctly marked. To this 

 process of progressive morphological change observed in the 

 growth of the individual the term ontogenesis has been ap- 

 plied. 



No Successive Stages of Functional Activity seen in Phylo- 

 genesis. A comparison of living forms with fossils arranged 

 in series in the order of their sequence in the rocks (i.e., chron- 

 ologically) has led to a belief that races, like individuals, 

 have their beginning, adolescence, maturity, and old age, and 

 the term phylogenesis was suggested by Haeckel to express 

 this idea. The fact must be emphasized, however, that in 

 individual development there is a change of function associ- 

 ated with the several stages of ontogenesis; while it is diffi- 

 cult if not impossible to imagine any corresponding change 

 of function in the successive representatives of a common race, 

 and while there are many analogies between the stages of 

 development of ontogenesis and the stages of evolution in 

 the history of organisms (pnylogenesis), great caution is neces- 

 sary not to force this theory of correspondence between the 

 ontogenetic stages of functional activity and the order of 

 differentiation of new characters expressed in the phyloge- 

 netic history of organisms. 



Contrast between the Developmental Stages of the Individual 

 and the Succession of Species. The two series of phenomena 

 present this marked contrast, that in the one (ontogenesis) 

 each particular phase of development is a repetition of phe- 

 nomena which have been repeated in the same way from the 

 beginning of organic life; in the other (phylogenesis) each 

 change is a step in advance of anything that has occurred 

 before ; the series is a single progressive series, with modifica- 

 tions and increment, but with no cycles of repetition. De- 

 velopment begins anew with each individual organism. 



