C. E. Beecher — Origin and Significance of Spines. 329 



Art. XXXIV. — The Origin and Significance of Spines : A 

 Study in Evolution; by Charles Emerson Beecher. 



[Continued from page 268.] 



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 only take place with 

 proper nutrition. Under local stimulus, the currents of the 

 circulation or forces of nutrition are set up in an organism 

 toward the center 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, 68 and the repetition of parts an almost universal 

 character among organisms, 5 it would appear that the foregoing 

 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 con- 

 dition 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 compound spine or a 

 group of spines. 



Carrying this repetitionary process to a maximum, there 

 would result a generally spinous condition. Asa possible illus- 

 tration of this, no class of organisms probably exhibits so many 

 kinds and series of repetitions of all sorts of external struc- 

 tures as the Echinodermata, and it is significant that this is a 

 typically spiniferous sub-kingdom. 



Except in a few classes of organisms, compound spines are 

 relatively rare as compared with simple spines. They are very 

 common among the Radiolaria, which furnish the greatest com- 

 plexity occurring anywhere in the organic world. (See Plate 



