ORIGIN AND SIGNIFICANCE OF SPINES 67 



have arisen by hypertrophy. After having thus originated 

 by growth force, they may or may not be of use for offence, 

 defence, or concealment, or in any way give their possessor a 

 distinct advantage. 



VII. By repetition. (B 2 .) 



Under the consideration of spine production by repetition 

 it is proposed to include local repetition or duplication of 

 spines on or about a primary spine, the limit of this repetition 

 resulting in a generally spinose condition. 



It has been shown that intermittent stimulus produces 

 growth, and furthermore that growth can take place only 

 with proper nutrition. Under local stimulus the currents of 

 the circulation or forces of nutrition are set up in an organism 

 toward the centre of stimulation. The nutrient matter is 

 brought to this point, and more or less of it is expended in 

 building up a structure which is the reciprocal or direct 

 resultant of the stimulus. Now, since all motion is primarily 

 rhythmic, 66 and the repetition of parts an almost universal 

 character among organisms, 5 it would appear that the fore- 

 going conditions would be favorable to the repetition or 

 reproduction of the structures. In this way it is easy to 

 account for the growth of spines that cannot be explained as 

 the direct result of external stimuli (A), or by any process 

 of decrescence (C, D). The nature of the influence seems to 

 be similar to induction in electrical physics, or to the force or 

 stimulus of example in human conduct. 



Stated as a concrete case, a simple spine produced by any 

 primary cause may be taken, and it will be granted that the 

 vital or physiological adjustments produced in its growth 

 and maintenance have brought about or induced an harmonic 

 condition in the adjacent tissues. Subsequent growth will 

 most naturally repeat the previous structures, so that in 

 addition to the primary spine there will be other smaller 

 spines on or about it, together constituting either a com- 

 pound spine or a group of spines. 



