356 0. E. Beecher — Origin and Significa/nce of Spines. 



forms. The numbers indicating chronology simply refer to 

 successive periods of time. In particular cases, they may be 

 long geologic ages as Cambrian, Ordovician, Silurian, Devonian, 

 and Carboniferous, or in other instances they may represent 

 much shorter periods. 



From the study of the ontogenies of spinose forms, it has 

 already been ascertained that they were simple and inornate 

 during their young stages ; and from the phylogenies of the 

 same and similar forms, it was likewise learned that they were 

 all derived from non-spinose ancestors. It has also been shown 

 that spines represent an extreme of superficial differentiation 

 which may become fixed in ontogeny, and the further conclu- 

 sion, that spinosity represents a limit to morphological and 

 physiological variation, has been reached. Finally, it is evident 

 that, after attaining the limit of spine differentiation, spinose 

 organisms leave no descendants, and also that out of spinose 

 types no new types are developed. 



Yale Museum, New Haven, Conn, June 1st, 1898. 



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