jANtJAEY29, 1897.] 



SCmNGE. 



167 



all their subsequent stages of development 

 throughout their lives, more perfect, more 

 decisive, as well as more obvious, than in 

 animals, like the vertebrata, which cari-y no 

 such burden of hard, dead parts upon, and 

 in which their stages of development are 

 recorded. The cycle of the ontogeny is, 

 therefore, not only physiological, but it is 

 also a definite series of structural changes 

 and is often accompanied by transforma- 

 tions of remarkable and sometimes startling 

 character. 



These retrogressive transformations in 

 old age of the shells of Cephalopoda, Brach- 

 iopoda and Pelecypoda have been found 

 to have decided correlations with the adult 

 characters of species that appear simul- 

 taneously or later in time. If one traces 

 any group through its evolution in time it 

 has, as stated by many authors, a period of 

 rise called the epaeme, a second period of 

 greatest expansion in numbers of forms and 

 species called the acme, and then usually a 

 movement towards contraction called the 

 paracme. All three of these terms were 

 first proposed by Haeckel, who used them 

 largely in a physiological or dynamical 



The paracme is the decline, and this takes 

 place through the reduction and actual loss 

 of structures and characteristics that have 

 been built up by evolution during the 

 epaeme. This is no ideal picture, but a 

 simple statement of the experiences of those 

 paleontologists who have patiently traced 

 the history of groups through geologic 

 time. Agassiz's law enables one to follow 

 the epaeme of the evolution of a species, or 

 genus, or order, or larger group, but further 

 correlations between the cycle of individual 

 life and those in the evolution of its own 

 genetic group must be sought in the corre- 

 lations existing between the older retrogres- 

 sive stages of the ontogeny and the paracme 

 of each group. 



The importance and peculiar nature of 

 these corelationsled me, in one of my papers, 

 to introduce, for this branch of research, the 

 term Bioplastology, which will be found 

 convenient by those interested in this class 

 of work. 



The following table of terms is useful 

 here to explain the relations of the cycle of 

 development in the individual to that of the 

 group to which it belongs. 



TEEMS OF BIOPLASTOLOGY EXPLAINING THE COEEELATIONS BETWEEN STAGES OP THE ONTOGENY AND 



THOSE OF PHYLOGENY. 



Ontogeny or Development Phylogeny or Evolution of the Phylum 



Structural oj. Structural oi „ t\„ ™;„„i 



Conditions ^^^^es Conditions ^^^^^ Dynamical 



f Embryonic Embryo or Foetal f Phylembryonic 



Anaplasis ■! Nepionic Baby Phylanaplasis \ Phylonepionic Epaeme 



L Neanic Adolescent I Phyloneanio 



Metaplasis Ephebic Adult Phylometaplasis Phylephebic Acme 



Paraplasis Gerontic Senile Phyloparaplasis Phylogerontic Paracme 



sense. The epaeme of any group, large or The dynamical terms are quoted from 



small, is usually a process of evolution by Haeckel and were used by him to designate 



addition of new structures or characteris- the phenomena of the rise and decline of 



tics based on older structures and thus lead- types, and also the terms anaplasis and 



ing to greater and greater complication of metaplesis. He, however, used ' cataplasis ' 



the primitive organization. The acme rep- in place of paraplasis, which is here pre- 



resents the time of greatest complication in ferred on account of the faulty derivation of 



structure and greatest expansion in num- cataplasis. 



bers of forms for any group, large or small, i He realized the importance of these phe- 



