C. E. Beecher — Origin and Significance of Spines. 3 



correlation commonly applied in ontogeny and phylogeny can 

 likewise be used in the study of spines and spiniferous species, 

 with equally exact results, whenever the principal factors are 

 understood. 



Law of Variation. 



Before undertaking any general or special examination of 

 the life histories and interpretation of spinose organisms, it is 

 desirable to consider briefly some of the biogenetic principles 

 which are considered to bear directly on the problems here 

 under discussion. 



First among these is the law of variation or change, which is 

 so generally recognized as to require but the briefest restate- 

 ment. 



The organic as well as the inorganic world is subject to all 

 the forces of nature, internal and external, molecular and 

 molar, and even a partial stability is gained only through a 

 regulated adjustment. In organisms, this change is momentary 

 and persistent, while in most inorganic substances, it is slow 

 and intermittent. The results of this continual readjustment 

 constitute modification, which maybe progressive or regressive, 

 continuous or discontinuous (in the sense of accelerated, uni- 

 form, or retarded). They are everywhere present and the 

 causes always operative. Throughout life, the individual 

 changes, and in addition varies from all other individuals. The 

 family, also, changes with time, and likewise differs from other 

 families. Variation is everywhere present. Moreover, it is 

 generally accepted, and is so taken here, that, in its results, this 

 variation is not haphazard, but is normally in accordance with 

 certain demands or in harmony with certain surroundings. 

 Whether an organism itself tends to vary in all directions, or is 

 chiefly subject to modifications from external forces, does not 

 alter the preceding statement. 



Cope 11 has considered variation as either physico-chemical 

 (molecular) or mechanical (molar). The influence of the first 

 is known as physiogenesis and of the second as kinetogenesis. 

 In the animal kingdom, the potency of kinetogenesis is greater 

 as an efficient cause of evolution ; while in the vegetable king- 

 dom, physiogenesis is apparently of more importance. 



The tendency of variation is always in the direction of the 

 establishment of an equilibrium between the organism and its 

 environment. However, the laws of the development of the 

 earth preclude the possibility of a constant environment, and 

 therefore a perfect, permanent, and uniform equilibrium between 

 life and surroundings is unattainable. 



The manner of variation is clearly defined as progressive 

 and regressive. Progressive variation is one of the essential 



