THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 21 
the life of an individual, and in accordance with these ideas designated the pro- 
gressive periods of expansion in the phylogenetic history of a group as the 
Epacme, the period of greatest expansion in number and variety of species and 
forms as the Acme, and the periods of decline in numbers of species, etc., as the 
Paracme. 
Haeckel used also the term Anaplastology for the physiological relations of 
the stages of progressive growth and those of the epacme of groups, Metaplas- 
tology for those of the adult and the acme of groups, and Cataplastology for 
those of the senile stages and the paracme of groups. These terms seem to 
cover the same ground as those we have employed, but they were in reality 
chosen for the purpose of classifying physiological relations. Thus the anaplastic 
relations of the neepionic and nealogic stages to the phenomena occurring dur- 
ing the epacme of groups, the metaplastic relations of the ephebolic stages to the 
phenomena occurring at the acme of groups, and the cataplastic relations of the 
geratologic stages to the phenomena occurring during the paracme of groups, are 
the functional relations of the structural modifications occurring in the ontogeny 
of individuals to those which are characteristic of the phylogeny of groups. 
THrory or RADICALS AND Morpno.ocicaL EquiIvVALENCE IN 
PROGRESSIVE Forms. 
The simpler characters of the sutures in the adults of more ancient forms, as 
compared with the more modern species of the same series, has been noticed by 
Wiirtenberger, Zittel, Neumayr, Waagen, and Branco,! in different groups of 
Ammonitine. The first is very decided in his statement, that the Ammonitine 
he has studied form perpetually diverging series, which spring from certain 
common ancestral forms. 
The constant repetition of discoidal and involute forms in series, which are 
otherwise distinct in respect to their sutures and minor characteristics of develop- 
ment and shell markings, produces a similarity in the succession of the forms. It 
is practicable to compare the evolution of discoidal into more involute forms of 
any one series with a similar genetic procession in any other series. Thus in the 
General Summary, Plate XIV., we can compare the discoidal forms of Ver. Cony- 
beari, Fig. 20, with Arn. tardicrescens, Fig. 26, Cor. rotiforme, Fig. 30, and Ast. Tur- 
nert, Fig. 36, and in the same way the involute forms of As/. Collenoti with Oayn. 
oxynotum, Greenough, and Lotharingum ; and these comparisons also hold good for 
Schlot. Boucaultiana, and the terminal forms like Woh. Emmerici and Psil. mesogenos, 
which are also involute. In exceptional series the whorls do not become more 
involute in the higher species, but are nevertheless modified in those character- 
istics which usually accompany and correlate with increase of involution. Thus 
the lateral diameter of the whorl decreases, the sides become more and more 
1 Wiirtenberger, Stammesgesch. d. Amm., Darwinistische Schriften, Nr. 5, Leipzig, 1880, p. 91. Zittel, 
Ueber Phylloceras tatricum, Jahrb. d. k. k. geol. Reichsant., 1869, p. 65, Neumayr, Die Phylloceraten d. 
Dogger und Malm, Ibid., 1871, pp. 347, 348; also, Zeits. d. deutsch. geol. Gesellsch., 1875, p. 866. Waagen, 
Die Formenreihe d. Amm. subradiatus, Benecke’s Geognost. paleont. Beitr., II. p. 202. Branco, Paleontogr., 
RXV 1 ROX VAT 
