STUDIES IN EVOLUTION 

 I 



GENERAL EVOLUTION 

 1. THE ORIGIN AND SIGNIFICANCE OF SPINES 



A STUDY IN EVOLUTION* 

 (Plate I) 



Introduction 



The presence of spines in various plants and animals is, 

 at times, most obvious to all mankind, and not unnaturally 

 they have come to be regarded almost wholly in the light 

 of defensive and offensive weapons. Their origin, too, is 

 commonly explained as due to the influence of natural selec- 

 tion, resulting in the greater protection enjoyed by spiuiferous 

 organisms. But when, upon critical examination, it is seen 

 that some animals are provided with spines which apparently 

 interfere with the preservation of the individual, that other 

 animals develop spines which cannot serve any purpose for 

 protection or otherwise, and that spines themselves are often 

 degenerate or suppressed organs, then it becomes evident that 

 the spinose condition may have other interpretations than the 

 single one of protection. 



The object of this article is to make a few observations 

 on spinosit}^ especially among invertebrate animals, and to 

 endeavor to arrive at some general conclusions relating to the 

 origin and significance of this condition. It is believed that 

 the results have a broader application than is at first apparent, 

 and underlie important laws and principles of organic evolu- 

 tion. In closely related species, the presence or absence of 



* Amer. Jour. Sci. (4), VI, 1-20, 125-136, 249-268, 329-359, pi. i, 1898. 



