C. JE. Beecher — Origin and Significance of Spines. 129 



the other orders was produced during the whole Silurian, 

 Devonian, and Carboniferous. 6 



As the classes, orders, and families are based upon the 

 physiological and important functional structural characters or 

 differences, it is evident that at or near the beginnings of their 

 life history is found the demonstration of the domination of 

 phylogenic over ontogenic characters. 



Conditions or forces affecting growth. — Since spines are 

 purely organic structures, their production must follow the 

 general laws of organic change. The forces considered as of 

 most consequence are two : (1) the external stimuli from the 

 environment, and (2) the energy of growth force. These, 

 with their opposites (la) the restraint of the environment, and 

 (2a) the deficiency of growth force, are believed to include the 

 chief active and passive causes, not only of spine production, 

 but of growth and decline in general. Correlating these four 

 causes with their constructive and destructive agencies, to- 

 gether with their extrinsic and intrinsic modes of action, as pre- 

 viously explained, there result (A) the external stimuli of the 

 environment as an extrinsic cause of concrescence ; (B) energy 

 of growth force as an intrinsic cause of concrescence ; (C) ex- 

 ternal restraint as an extrinsic cause of decrescence ; and (D) 

 deficiency of energy of growth force as an intrinsic cause of 

 decrescence. The remaining vital forces (nerve force, or 

 neurism, and thought force, or phrenism) are not primary, 

 and, although doubtless affecting growth in higher organisms, 

 cannot be original causes applicable to all forms of life, both 

 plant and animal. 



In tabular form, the divisions and relationships of the fac- 

 tors of spine genesis may be expressed as follows : 



A 



r j extrinsically ) from external 



! ( (centripetally) ) stimuli 

 f Constructive agencies j 

 (concrescence) acting 1 B 



j intrinsically ) from growth 



^ ( (centrifugally) ) force 

 Spines originate by J ^ 



j extrinsically ) from external 



f l (ceniripetally) \ restraint 

 I destructive agencies J -p. 



I (decrescence) acting ■ , intrinsicalIy , f rom de fi c iency 



I (centrifugally) \ of growth force 



Under the last four divisions (A — D), it is proposed to discuss 

 the origin of spines, and from the observations made, to derive 

 certain conclusions regarding the significance of the spinose 

 condition. 



