168 



SCIENCE. 



[N. S. Vol. V. No. 109. 



nomena and also the significance of the 

 structural characteristics of decline, but did 

 not trace out the distinct correlations which 

 are claimed as fundamentals in bioplas- 

 tology. 



The terms anaplasis, etc., and their cor- 

 respondence, phylanaplasis, are the struc- 

 tural correlatives of dynamical terms, ep- 

 acme, etc., and will be found useful when 

 the statical phenomena or structures are 

 mentioned or contrasted with the dynamical 

 phenomena, or with periods of time in 

 which they occur, since the terms epacme, 

 acme and paracme also refer to time. 

 Terms of the ontogeny are placed opposite 

 to their correlatives in the column of phy- 

 logenetic terms, but in reading the table it 

 should be clearly understood that the in- 

 dividual whose life history is represented 

 by the first three columns is supposed to 

 have been taken from the midst of those 

 that lived during the acme of the phylum 

 and belonged to a phylephebic species. In 

 studying the development of such an in- 

 dividual it has been repeatedly observed 

 that the embryo repeated the adult char- 

 acters of the most ancient representatives 

 of the phylum, which are here called in 

 accordance with this evidence, phylem- 

 bryonic. 



It has also been ascertained that there 

 are full-grown types in the epacme and 

 acme of groups which correspond to the 

 transient nepionic or baby stage of those 

 that occur later in time ; these are the 

 phylonepionic ; others have similar corre- 

 spondences with the neanic stages and are 

 properly designated as phyloneanic types 

 or forms. The structures of the ephebic 

 (adult) stage are essentially the differ- 

 entials of the time and fauna in which they 

 occur, and necessarily have no correlations 

 with the past. Their relations are obvioi\sly 

 and wholly with the present, except in so 

 far as they represent the consummations 

 of evolution in structures. The structural 



changes in the gerontic stage of the indi- 

 vidual are repeated with sufiicient accuracy 

 in the adult, and often even in the neanic 

 stages of types that occur in the paracme of 

 the evolution of a phylum, so that one is 

 forced to consider seriously whether they 

 may not have been inherited from types 

 that occur at the acme of the same group. 

 The fact that these changes occur first in 

 the ontogeny during the gerontic stage does 

 not necessarily imply that they first make 

 their appearance after the reproductive 

 period. No gerontic limit is known to the 

 reproductive time in the lower animals, and 

 it may well be that the continual recur- 

 rence of gerontic stages in individuals dur- 

 ing the epacme of groups may lead to their 

 finally becoming fixed tendencies of the 

 stock or hereditarj' in the phylum, and thus 

 established as one of the factors that oc- 

 casion the retrogression or paracme of 

 groups. The paracme may also be con- 

 sidered as occasioned by changes in the sur- 

 roundings from favorable, as they must 

 have been up to acmatic time to unfa- 

 vorable during the succeeding paracmatic 

 period in evolution. Still a third supposi- 

 tion is also possible, viz., that the type, like 

 the individual, has only a limited store of 

 vitality, and both must progress and retro- 

 gress, complete a cycle and finally die out, 

 in obedience to the same law. 



All of these views can be well supported, 

 but, whatever may be the true explanation, 

 it is obvious that there are plenty of parac- 

 matic types, which, in their full-grown and 

 even in their neanic stages, correlate in 

 characters and structures with the charac- 

 ters and structures that one first finds in 

 the transient gerontic stages of acmatic 

 forms of the same type. These can, there- 

 fore, be truthfully and accurately described 

 as phylogerontic in the phylum. 



In other words, one is able to apply 

 gerontic changes in the ontogeny to the 

 deciphering of the true relations, the ar- 



