IS93-J y t [Hyatt. 
cases of retrogression in wliich 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 wliole of the 
uepionic stage. There are also some examples among parasites in 
which progression seems to have been i-educed so much that one 
can say it is practically eliminated from all stages succeeding some 
of the earliest embryonic. For such forms as these the proper 
term would be Pakaplasis from •n-apairXao-o-w, 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 tlieir own type or allied t^'pes, 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 continuitj^ 
in time invariably accompanied by change, but whetlier the modi- 
fication be progressive or retrogressive, or a combination of 
progression and retrogression, is immaterial. It is obviously 
better not to use these terms for ontogenic phenomena. There 
are sufficient terms in "development," "diffentiation of charac- 
teristics," "rise," and one has always a slight mental reservation 
in employing this word for the growth and development of an 
individual or isolated zoon. 
"Metaplasis oder umbildung (transvolutio)" is used by tlie 
same eminent authority for the adult period in a general sense, 
and it appears to the writer to have useful function as a descrip- 
tive term especially, since it is unifoi*m witli anaplasis and para- 
plasis. Thus one can describe the metaplastic phenomena or 
characteristics of the ephebic stage in any form as meta])lasis, and 
also speak of the general meaning of metaplasis without referring 
to tliat stage of ontogeny in any special form. The use of 
"transvolutio" is obviously objectionable, since it introduces 
confusion and conflicts with the proper definition of "evolutio" 
or evolution as given above. 
"Cataplasis oder riickbildung (involutio)," used by Haeckel 
for the senile stage, is open to the objection that there is no cor- 
responding Greek word, and also that KaraTrXdo-o-o), the only Greek 
verb to wliich this term can be referred, means to spread over or 
plaster. Paraplasis, derived from TrapairXdo-o-w, meaning to change 
the form for the worse or deform, is an obviously preferable 
designation. Thus the paraplasis or paraplastic phenomena of all 
PROCEEDINGS B. S. N. H. VOL. XXVI. 7 AUGUST, 1893. 
