391 
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. 
chia al Ananepionic. 
2. Nepionic. 4 Metanerfonie. 
Anaplasis. S oung. Paranepionic. 
Immature (omenecanic. 
(or 5. Neanic. Metaneanic. 
nla ireat tt Paraneanic, 
Mature Anephebie. 
Metaplasis. | or 4. Ephebic. { Metephehic. 
Adult. Parephebic. 
{ Senile Anagerontic. 
Paraplasis. - or 5. Gerontic. { Netagerontic, 
( Old. 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, 
atffer 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,” ete., and to these Jackson added Phylembryo in his Phylogeny of the Pele- 
cypoda, p. 289. 
