I893-] ^ ' [Hyatt. 
Ctetology should also, however, include the study of the action 
of physical forces when they either actually do produce direct 
effects upon organisms, or may he assumed to act in this way. 
The action of changes in light, food, heat, and moisture may 
yet be proven to cause modifications that cannot be included 
under the head of entergogenic reactions without dunger of 
confusion. 
Maupas gives exceedingly instructive examples of this class and 
quotes other authorities who have investigated their effect in 
Protozoa. 
Beddard gives a number of exam])les of such modifications in 
his "Animal coloration," and Semper has also discussed the same 
subject more extensively in '-Die naturlichen existenzbedingungen 
der thiere." 
The use of the term entergogenesis would make it practicable 
to indicate the essential distinction existing between the modifica- 
tions produced by internal forces and those arising as the direct 
results of physical or chemical action by means of the antithetical 
term ectergogenesis and ectergogenic, and both of these w^ould 
then be included undei- Ryder's term ergogenesis. 
These explanatory remarks serve to show that this is a branch 
of research which needs to be isolated from auxology and genesi- 
ology since it is devoted to the study of the origin of ctetic char- 
acteristics and therefore necessarily considers all of the internal 
reactions of the organisms in response to the action of j^bysical 
forces, as well as the more obscure reactions of structures which 
are produced by (or sui)posedto be produced by) the direct phys- 
ical or chemical action of external ])hysical forces alone. 
To sum up the objects of ctetology as has been done with 
growth and genesiology, it may be briefly stated as dealing with 
all the characters that arise from the union of two factors, the 
physical stimuli of the environment and the reactions of the 
organism. 
BlOPLASTOLOGV. 
The separation of auxology and genesiolog}^ and ctetology shows 
also the study of the correlations of ontogeny and phylogeny to 
be distinct from anv one of these, and this branch of research can 
