ORIGIN AND SIGNIFICANCE OF SPINES 97 



the most evident, marker of the attainment of these limits. 

 The presence of a spine on an organ or part indicates the 

 limit of progression or regression of that part or organ. If 

 the spinose condition is general, or if it dominates important 

 functions, it then indicates the limit of progression and regres- 

 sion of the organism. 



Spinosity the Paracme of Vitality. 



The physiological interpretation of spinosity is a correlative 

 of the morphological aspect of the same condition, and, as it 

 was found that spinosity was a limit to morphological progress 

 or regress, it will now be shown that it also indicates the par- 

 acme or decline of physiological progress. Both inferences 

 are drawn from the individual or ontogenetic standpoint, as 

 well as from the racial or phylogenetic. 



In the spinose individual the decline of vitality has been 

 studied by Geddes 20 in thorny plants. He concludes that 

 they show a " gradual death from point backwards (i. e. ebbing 

 vitality}" The requisite evidence is afforded in the experi- 

 ence of gardeners who generally consider spiny plants as 

 " always given to die back," or, as otherwise expressed, they 

 " often prune themselves." It is difficult to adduce the same 

 kind of evidence among animals, though there may be some 

 degree of semblance between this self-pruning of spiniferous 

 plants and the growth, death, and shedding of the antlers of 

 the modern Deer. Stronger evidence of the relations of 

 spinosity to the organism is afforded in the consideration 

 of spines as consisting wholly of the mechanical tissues. 

 They are more or less dead structures and are usually with- 

 out special physiological function. Hence, in so far as the 

 whole or a part of an organism is spinose, it represents the 

 ratio between the mechanical and active tissues, or between 

 the inert and living structures. 



Morris 49 correlates the mechanical and motor defences of 

 animals and plants in a manner bearing upon this subject as 

 follows : " If we examine the whole range of the animal 

 kingdom, we find every phase of combination of mechanical 



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