CYCLE IN THE LIFE OF THE INDIVIDUAL (ONTO- 

 GENY) AND IN THE EVOLUTION OF ITS 

 OWN GROUP (PHYLOGENY).* 



By Alpheus Hyatt. 



Presented October 14, 1896. 



The organic cycle, as generally understood both by laymen and 

 scientists, and as usually described in literature, is, as a rule, considered 

 from a physiological rather than a structural point of view. The develop- 

 ment of the young, and the attainment of the adult or comparatively 

 permanent stage, complete the progressive stages. Old age, accompanied 

 by losses of characteristics and functions and consequent weakening of 

 the body, is retrogressive, and brings on second childhood, thus complet- 

 ing the cycle in the ontogeny. 



My purpose to-night is to show that the cycle is also represented in 

 the life history of the individual by definite structural changes, and that 

 these have direct correlations with the history of the changes in the 

 forms of the group while evolving in time.f 



The fundamental discoveries that are more than any other directly 

 useful in the study of the phenomena of the cycle, both in ontogeny and 

 phylogeny, may be briefly noticed as follows. 



The opinion that the higher animals are complex colonial aggregates 

 of cells, which in structure are equivalents to the lowest and minutest 

 adult forms of the animal kingdom, the unicellular bodies of Protozoa, 



* This paper was in part read before the Academy as a general summary of tlie 

 phenomena of cycles, but does not assume to be an exhaustive or even complete 

 account of the literature or theoretical views treated of. 



t These correlations have been more fully stated in a number of publications by 

 the author, especially " Genesis of the Arietidas," Smithsonian Contribution 673, and 

 Mem. Mus. Comp. Zoology, Vol. XVI. ; " Bioplastology and the Related Branches 

 of Scientific Research," Proc. Bost. Soc. Nat. Hist., Vol. XX VI. ; and "Phylogeny 

 of an Acquired Characteristic," Proc. Am. Phil. Soc. Vol. XXXII. No. 14.3. 



VOL. XXXII. 14 



