94 GEOLOGICAL BIOLOGY. 



nomic rank, as the specific characters, are of most recent 

 origin and their geological range is of the shortest duration. 

 In studying fossils, therefore, and using them as time-indi- 

 cators, or studying the history of the organisms represented 

 by them, it is all-important to notice the taxonomic rank of 

 the morphologic characters under consideration, since it is 

 true that the less the taxonomic value of the character the 

 sharper and more diagnostic is its time-value. 



Although the successive eras are distinguished by change 

 in the specific and in the generic types of organisms, and it 

 may be supposed that some of them at each era are directly 

 descended from those of different species of a previous era, 

 it is not so clear that the succession should present any 

 analogy to the succession of morphologic form exhibited by 

 the individual in its various stages of growth, as will be seen 

 by the following considerations. 



Stages of Growth in Ontogenesis. In the growth of the 

 individual there are certain stages called (i) infantine, or 

 larval, (2) adolescent, (3) adult, (4) senile, which may be 

 sharply distinguished by morphological characters, and dur- 

 ing the life of the individual by distinct physiological opera- 

 tions. These stages are found by Hyatt and others to be 

 so characteristic of the period of time in the growth as to be 

 precisely named ; Bather* has called them terms of auxology. 

 Hyatt, in a later article, f suggests the propriety of using 

 the term bathmology, first proposed by Cope, for this 

 classification of the stages of individual growth. The 

 technical names proposed by Hyatt are slightly modified 

 by Bather, and are as follows, viz., the infantine or larval 

 stage or form is called embryonic and brephic, the adolescent 

 stage is called neanic, the adult stage is ephebic, the old age 

 or senile stage of development is called gerontic, with a de- 

 clining, catabatic, and an hypostrophic or atavic substage. 

 Bather proposed the application of these terms to the tem- 

 poral stages in individual development by the addition of the 

 prefix morpho thus morphephebic to denote the characteristics 



* ZooL Anzeigcr, Nov. 14 and 28, 1892, pp. 420, 424. 

 f Proc. Boston Soc. Nat. Hist., xxvi. p. 61, etc., 1893.. 



