C. E. Beecher — Origin and Significance of Spines. 355 



generic, and sometimes of family rank, or even higher. They 

 have therefore acquired a fixed importance in these special 

 groups, and are recognized in the same categories with physio- 

 logical and structural characters. The differences which appear 

 at an early period in higher genera are the bases of distinction 

 among lower genera. If the spines or other similar features do 

 not make their appearance in an individual until a late adoles- 

 cent stage, they are usually of negative value in a scheme of 

 classification. This agrees with the general principle recently 

 suggested by Harris, 32 that when the main features of the orna- 

 ment (= spines, etc.) are foreshadowed in the larval and early 

 adolescent stages, they are to be regarded as of taxonomic 

 value. 



Ontogeny 

 stages. 



Ontogeny- 

 condition. 



Phylogeny 

 stages. 



Phylogeny Chron- 

 condition. I ology. 



Old age or 

 gerontic 



Paraplasis Phylogerontic Paracme 



Adult or 

 enhebic 



Metaplasis Phylephebic Acme 



Immature 



or neanic 



Anaplasis Phyloneanic Epacme 



Larval or 

 nepionic 



Anaplasis 



Phylonepionic Epacme 



Embryonic 



Anaplasis Phylernbryonic Epacme 



Diagram and table showing correlation of stages and conditions of development 

 in the spinose individual, in its ancestry, and in time. 



The preceding diagram illustrates the previous statements, 

 and shows the correlation between the stages and conditions of 

 growth in the ontogeny of a spinose individual, with its phylo- 

 geny, and also the chronology of groups containing spinose 



