C. E. Beecher — Origin and Significance of Spines. 257 



most of these cases, the rib represents the progression of a fold 

 in the edge of the mantle, while the spine is a process of a con- 

 centric lamina, and is usually more or less flat or tubular. 

 Occasionally, the rib becomes obsolescent, and is represented 

 by a row of spines, as in some specimens of the Gastropod, 

 Crucibulum spinosum. When the radiating and concentric 

 ornaments are distinctly continuous, a reticulate or cancellate 

 appearance is produced, and the points of intersection often 

 bear spines ; as in Aviculopecten scabridus, 29 A. ornatus™ 

 Actinopteria Boydi™ Pterinopecten sjiondylus™ etc. 



The raised lines or ridges on the legs and carapaces of Crus- 

 tacea are frequently spiniferous, as Gelasimus princeps, Gecar- 

 cinus ruricola, etc. The radii on the shells of barnacles are 

 sometimes differentiated into spines ; as in Balanus tintinnalm- 

 lu?n var. spinostis. 13 



In the higher animals, the differentiation of ornamental 

 features into spines is not common, especially as most of the 

 forms are devoid of hard external parts. Among the fishes 

 and reptiles, certain lines and ridges on the head and body are 

 often spiniferous, while in others the scales have spiniferous 

 ribs. 



III. Secondarily as a means of protection and offense. (A 3 , B 4 .) 



After spines have originated through the stimuli from the 

 environment acting on the most exposed parts, or by growth 

 force, or by progressive differentiation of previous structures, 

 they may often acquire added qualities, one of which is to 

 protect an organism from the attacks of many of its enemies. 



Morris 49 shows that defense in animals is either mechanical 

 or motor, while in the higher plants, it is purely mechanical. 

 The spine clearly belongs to the mechanical mode of defense, 

 and in many animals may be efficient without motion. If 

 motion is added, it then may serve not only for protection but 

 for offense as well. Natural selection evidently could not 

 originate a spine, but after one has appeared from any of the 

 causes mentioned in the preceding paragraph, this agency 

 could tend to preserve and allow the spine to develop along 

 certain lines. The restrictions as a defensive structure would 

 be those of efficiency, and therefore all the monstrous growths, 

 vagaries, and ornamental spine features would arise independ- 

 ently of the action of protective selection, and would be 

 accounted for by the operation of the forces of the environ- 

 ment, growth, and sexual selection. In this way, the simple 

 antlers of the Tertiary Deer may be imagined to have reached 

 the highest degree of efficiency as weapons, by ordinary natural 

 selection (figure 41). In most cases, the subsequent increasing 

 complexity of the antlers during more modern times cannot 

 have improved their usefulness for protection or fighting 



