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genesis, that not only can one indicate the past history of groups 

 from the study of the young, and obviously the present or existing 

 progression or retrogression of the type by means of the adult char- 

 acters of any one organism, but that it is also possible to prophecy 

 what is to happen in the future history of the type from the study 

 of the corresponding paraplastic phenomena in the development of 

 the individual. 



Whether these claims are well founded or not the nomenclature 

 to be employed is a matter of importance and should be accurate, 

 appropriate and convenient for those who are interested in this 

 work. 



Ontogeny. Table I. 



CONDITIONS. STAGES. 



STAGES. 



SUBSTAGES 



SUBSTAGES. 



/ Embryonic. 



1. Embryonic. 



Several.* 



No popular names 



I Larval 





r Ananepionic. 





\ or 



2. Nepionic. 



\ Metanepionic. 





Anaplasis. ( Young. 





^Paranepionic. 





/Immature 





/•Ananeanic. 





f or 



3. Neanic. 



< Metaneanic. 





\ Adolescent. 





vParaneanic. 





r Mature 





/ Anephebic. 





Metaplasis. < or 



4. Ephebic. 



< Metephebic. 





I Adult. 





v Parephebic. 





r Senile 

 Paraplasis. < or 

 I Old. 





/-Anagerontic. 





5. Gerontic. 



-< Metagerontic. 







v Paragerontic. 





Recent researches have, in my opinion, clearly demonstrated that 

 all the stages of development like the embryonic will have to be sub- 

 divided in studying many groups. These subdivisions are also rela- 

 tively important and their differences are often well defined. 



The ovum and the extreme degraded substage of the senile period 

 represent the widest departures structurally and physiologically 

 from the adult, one being at. the commencement and the other the 

 termination of ontogenesis. Departing from the ephebic stage 

 in either direction towards these extremes one finds the same law. 

 Contiguous substages of development, when considered in sequence, 

 differ less from each other and from the adult the nearer they are to the 

 ephebic stage, and they differ, on the other hand, more from the adult 

 and from each other in structure and form the nearer they are to the 



* These stages were enumerated and more or less described under the names of Prot- 

 embryo, Mesembryo, Metembryo, Neoembryo, Typembryo in my paper on " Values in 

 Classification," etc., and to these Jackson added Phylembryo in his Phytogeny of (!: 

 cypoda, p. 289. 



