STUDIES IN EVOLUTION 



spines seems in itself a trivial character, indicating at best 

 only specific differences, yet it will be shown that the spines 

 are often the expression of important vital adjustments and 

 conditions, and are not merely external features of the same 

 value a& 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 

 significance? It must be granted at the outset that apart 

 from other characteristics, or when regarded as simple spini- 

 form extensions of certain tissues or organs, they have no 

 such value or meaning. How, then, should they be con- 

 sidered ? 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 be 

 shown, a stage of evolution, 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 practi- 

 cally 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. 



