393 
nomenclature which has been here adopted, with some necessary 
changes. 
The dynamical relations of three great phases of evolution in the 
phylum were designated by Haeckel * as the efacme, including the 
rise of the type from its origin, the acme, meaning the period of its 
greatest expansion in members and forms, and the paracme, or de- 
cline towards extinction, and these phenomena were correlated with 
the similar physiological phenomena of the ontogeny, and these 
appear in the table of phyletic terms given below. 
Previous to this, in the same volume (p. 76), Haeckel gives his 
classification of the development of the individual under three 
headings: ‘‘Anaplasis oder Aufbildung (evolutio),’’ meaning 
thereby to include the physiological phenomena of all of the stages 
developed in the four earlier stages of the individual. This is cer- 
‘tainly a useful term for the entire series of transformations from the 
fertilization of the ovum until the progressive stages are all passed 
through. It does not express nor can it be used for cases of retro- 
gression in which degenerative characters are introduced at such an 
early age that progression is limited to the embryonic, or to that 
stage and a part or the whole of the nepionic stage. There are 
also some examples among parasites in which progression seems to 
have been reduced so much that one can say it is practically elim- 
inated from all stages succeeding some of the earliest embryonic. 
For such forms as these the proper term would be Paraplasis, from 
mapa mAdoow, meaning to change the form for the worse, to deform. 
Thus the stages of such forms could be collectively spoken of as 
paraplastic with relation to the ontogeny of others of their own type 
or allied types, whereas they could not be described as anaplastic. 
The explanatory word ‘‘ evolutio’’ is here used by Haeckel in a 
confined and erroneous sense. Evolution really means continuity 
in time invariably accompanied by change, but whether the modi- 
fication be progressive or retrogressive, or a combination of pro- 
gression and retrogression, is immaterial. It is obviously better not 
to use these terms for ontogenic phenomena. There are sufficient 
terms in ‘‘development,’’ ‘‘differentiation of characteristics,’’ 
‘‘rise,’’ and one has always a slight mental reservation in employ- 
ing this word for the growth and development of an individual or 
isolated zo6n. 
? 
* Morphologie der Organismen, Vol. ii, pp. 320-366. 
PROC. AMER. PHILOS. SOC. XXXII. 148. 2 x. PRINTED JUNE 5D, 1894. 
