0. E. Beecher — Origin and Significance of Spines. 13 



organisms presents greater variety, and many of the forms are 

 repeated again and again, not only in various species of this 

 group, but elsewhere both in the animal and vegetable king- 

 doms. 



Whenever the development of a compound spine can be 

 studied, it shows a gradual progress from the simple to the 

 complex (figures 21-23). The antlers of the Red Deer (Cervus 

 elapkus) furnish a familiar example. Fawns of the first year 

 have antlers with only a single prong, a short front tine being 

 added the second year ; then " year by year as they are 

 renewed they acquire a greater and still greater number of 

 tines and branches, till they finally attain the complete stage, 

 when their owner is termed a ' royal hart'" 44 (figure 16). 

 Although somewhat conventionalized, the primary series of 

 spines on the Spondylus shown in figure 20 exhibits the pas- 

 sage from simple to compound forms. An inspection of many 

 species of Murex will show the stages in series presenting a 

 greater complexity. 



After spine development has reached its maximum growth 

 and differentiation, evidence of old age may be exhibited in 

 two ways: {a) The spines may be reduced by resorption, 

 decay, or abrasion, an.d finally become obsolescent ; or what is 

 of greater import (b), they may gradually cease to be devel- 

 oped, as is especially shown in organisms in which spine growth 

 is by serial repetition. Thus, in Spondylus calcifer, a young 

 individual measuring about two inches across has marginal 

 spines fully an inch in length. Even longer spines are found 

 when the shell reaches a width of four inches. On attaining 

 a maximum diameter of about six inches, spine growth gradu- 

 ally ceases, and the margin of the valves is entire and nearly 

 smooth. At this stage, shell secretion is confined to excessive 

 thickening of the valves. These senile stages of spine growth 

 will receive further consideration under the discussion of 

 ontogeny and phylogeny of spinous species. 



Application of law of morphogenesis. — The manner in 

 which spines arise from plane surfaces, or from the growth or 

 modification of superficial structures, and also through the 

 decadence of organs, has now been noticed. The spine may 

 thus be taken as a unit for comparison, and its various stages of 

 growth, which were shown to have a definite sequence, may be 

 used in correlation to determine relatively the degree of spine 

 specialization attained by any organism. Furthermore, enough 

 data have been already given to lead to the suspicion that 

 spines may represent the limits of ornamental or superficial 

 differentiation or variation. At this point in the discussion, 

 this statement must be considered as more suggestive than 



