260 C. E. Beech er — Origin and Significance of Spines, 



the ground, lie finds the body usually smooth, while those feed- 

 ing on trees or on both trees and ground are often variously 

 spined and tuberculated. These ornamental features arise 

 from the modification of the piliferous warts common to all 

 lepidopterous larvae, and he concludes that the trees were 

 more favorable for temperature, food, etc., than the ground, 

 and that an increase of nutrition and growth force led to the 

 hypertrophy of these warts into tubercles and spines. Having 

 thus arisen, they immediately became useful for protection 

 from birds and parasitic insects. 



Among the Crustacea, there are also numerous examples of 

 protective spines. These may be confined to parts of the body 

 and legs especially exposed, or the entire animal may partake 

 of the spiny character, as in the crab, Echidnocerus setiman us, 

 where even the eye-stalks and antennae are spiniferous. Others, 

 like Lithodes maia, have the spines generally distributed over 

 the carapace and. legs. "While serving for defensive purposes, 

 this generally spinose character has probably reached its 

 extreme development through the influence of repetition (B 2 ). 

 The nauplius larva of Lep as fascicular is is very large, and 

 has highly defensive spines which are explained by Balfour 3 as 

 a secondary adaptation for protection. The larger spines on 

 Trilobites, especially those from the genal angles and the axis, 

 doubtless served protective purposes. The extremes of spi- 

 nosity in this class are found in the various species and genera 

 of the family Acidaspidae, and also in many forms of Arges, 

 Terataspis, Hoplolichas, etc. 



Even among the star- fishes, which are so generally spinose, 

 some forms have the spines so prominently developed on the 

 most exposed portions of the animal that they evidently serve 

 for protection ; as Acanthaster Solaris, Echinaster spinosus, 

 etc. 



The examples already given are sufficient to emphasize the 

 fact that after spines are developed, they may then often serve 

 for protection and offense and therefore be useful, their effi- 

 ciency being controlled by natural selection resulting in the 

 survival of the fittest. 



Another process or kind of selection has been described by 

 Yerrill, as " Cannibalistic Selection." He has shown that the 

 young of carnivorous animals often prey upon each other, as 

 in the larval forms of some Decapoda, or sometimes even before 

 the escape of the young from the egg capsules, as in some of 

 the Gastropoda. Here, of course, any natural variation in 

 the newly-hatched animals which would give an individual 

 some advantage over its companions would tend to its pre- 

 servation and to their destruction. In this way, it may occur 

 that the relative growth of spines in the zoea of decapods has 



