Introduction 17 



nemertean or fish constitutes a physical or physico-chemical 

 (including it may be a complex physico-chemical or organic) 

 action, the ultimate behavior of each animal to such con- 

 stitutes a proenvironal reaction or response. 



IV. SELECTION or selective survival. 



This contributory factor to the great Law of Penta- 

 morphogeny has been so fully dwelt upon by Darwin, 

 Wallace and subsequent students, that only a few notes 

 need be added here. In its actual and exact working as a 

 phase of Pentamorphogeny, it has not unfrequently been 

 brought in to explain facts that pertain to the other four 

 phases, and in its strict application it is largely a secondary 

 or derived factor that depends on the earlier action of 

 some one of the four other factors. Thus the plates and 

 spicules of some nemertean and of some primitive fish 

 species are primarily chitinous or calcareous deposits within 

 cell cavities, that represent superfluous products of meta- 

 bolism. But disliked by opposing animals, and offering a 

 certain resistance in attack, those forms have slowly become 

 dominant in which the deposits have increased in amount 

 and in exactness of deposition. Then the process of natural 

 selection steadily proceeded, till now only the cyclostomes, 

 and a few simplified scaleless derivatives from originally 

 scaled types of fish, represent groups that survive by shelter- 

 ing in mud, in sand, in holes, or as for the Hag Fishes by 

 exudation of abundant mucilage and adoption of a parasitic 

 habit. 



The abundant secretion of mucus, the evolution of elec- 

 tric organs, the production of defensive or of — as in the 

 chimaeroid sharks — offensive spines, are* in part proenvi- 

 ronal adaptations, but secondarily become of prime im- 

 portance in the life-struggle, as being conditions that favor 

 perpetuation of the species which develops these to the most 

 appropriate degree. Similarly the protective coloration, 

 alike as an offense and as a defense arrangement, seems to 

 represent primarily a proenvironal response to the action 

 of certain surrounding light rays, but secondarily may de- 

 termine, by action of natural selection, either the continued 

 life or the death of a species. 



