2 C. K Beecher — Origin and Significance of Spines. 



as color and many other skin or superficial characters. As 

 will be indicated later on, spines may also arise through the 



operations of a number of forces and conditions, and it may 

 well be asked, therefore, — Do spines have any profound signifi- 

 cance? It must be granted at the outset that apart from other 

 characteristics, or when regarded as simple epiniform exten- 

 sions of certain tissues or organs, they have no such value or 

 meaning. How, then, should they be considered 2 The reply 

 is evident: Their importance lies not in what they are, but in 

 what they represent. They are simply prickles, thorns, spines, 

 or horns ; they represent, as will he shown, a stage of evolu- 

 tion, a degree of differentiation in the organism, a ratio of its 

 adaptability to the environment, a result of selective forces, 

 and a measure of vital power. 



After studying numerous organisms, the writer is led to 

 believe that in every case no single reason is sufficient to 

 account for this spinose condition. The original cause may 

 not be operative through the entire subsequent phylogeny, so 

 that spines arising from external stimuli and then serving 

 important defensive purposes may at a later period practically 

 lose this function ; or spines may become more and more 

 developed simply by increasing diversity of growth forces, or 

 through the multiplicity of effects. In this way, causes may 

 follow, overlap, or even coincide with each other ; but in 

 interpreting special cases, the problems involved may be quite 

 complicated and often obscure. 



In reviewing the development of animal life from the 

 earliest Cambrian to the present, one cannot avoid being 

 impressed by the groups of spinose forms which appear here 

 and there throughout geologic time, and give a special phase to 

 contemporary faunas. Tracing these one by one through their 

 geological development, it is noticed that each group began its 

 history in small, smooth, or unornamented species. As these 

 developed, the spinose forms became more abundant until after 

 the culmination of the group is reached, when this type either 

 became extinct or was continued in smaller and less specialized 

 forms. In applying this principle to any order of plants or 

 animals, several precautions are necessary. The estimate must 

 be based approximately upon the general average of the total- 

 ity of specific characters, whether a genus, family, order, or 

 even a class is being considered. A short-lived family or 

 genus, or the terminal members of specialized groups, there- 

 fore, cannot be taken as representing the developmental status 

 of the larger divisions, because they culminated and disap- 

 peared independently of the culmination of the -class to which 

 they belong. On a small scale, however, each epitomizes the 

 rise and decline of the larger group, and the principles of 



