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



features were the chief variables. The stimuli which, during 

 the early life history of a group, were expended in internal 

 or physiological adjustments, later produce external differentia- 

 tion, and in this differentiation, spinosity is the limit. The 

 presence of spines, therefore, indicates the fixity of the primary 

 physiological characters, together with the consequent inability 

 of the organism to change due to its decreasing vitality. 



Conclusion. 



Just as all our features of terrestrial topography are included 

 between the limits of plains and mountains, and the moun- 

 tains are considered as the limit of progressive accidentation, 

 so the spines of animals or the monticules and pinnacles 

 of their surface may be considered as the limits of progressive 

 differentiation. The primitive base level, or peneplain, 

 becomes elevated, and by erosion is cut up into table lands, 

 mesas, and buttes, with intersecting valleys. The valleys are 

 gradually deepened, and the country becomes rougher until a 

 maximum is reached. Then follows a reduction of the inequali- 

 ties of the surface, and finally in old age, the smooth, gently 

 rounded outlines of geographic infancy again appear. So in 

 organisms, the smooth rounded embryo or larval form progres- 

 sively acquires more and more pronounced and highly differen- 

 tiated characters through youth and maturity. In old age, it 

 blossoms out with a galaxy of spines, and with further deca- 

 dence produces extravagant vagaries of spines, but in extreme 

 senility comes the second childhood, with its simple growth 

 and the last feeble infantile exhibit of vital power. 



The history of a group of animals is the same. The first 

 species are small and unornamented. They increase in size, 

 complexity, and diversity, until the culmination, when most of 

 the spinose forms begin to appear. During the decline, extrav- 

 agant types are apt to develop, and if the end is not then 

 reached, the group is continued in the small and unspecialized 

 species, which did not partake of the general tendency to 

 spinous growth. 



Lastly, it must be determined whether spines are really 

 hereditable characters, and therefore can be used in studying 

 the phylogenies of groups. No one has yet been able to show 

 any type or set of characters which cannot be transmitted from 

 parent to offspring. Hyatt 34 says : " Everything is inherited 

 or inheritable, so far as can be judged by the behavior of char- 

 acteristics." Furthermore, in a review of auimal life, extinct 

 and living, no one can fail to be impressed with the' fact that, 

 especially near the close of the life history of a group, or in a 

 series of highly specialized forms, spinose characters are often 

 considered as of supra-varietal value, and are rated of specific, 



