3-18 



SCIENCE. 



[N. S. Vol. XIV. No. 348. 



by high tide and devoid of living vegetation. 

 Above that is a narrow zone — the middle 

 beach — covered with debris of storms, sup- 

 porting a* few annual plants, and bounded 

 above by a storm-cut bluff. Above is the 

 upper beach, covered with a perennial, 

 sand-loving vegetation. On the lower beach 

 the zonal distribution of animals is striking. 

 Just above the water are found the scaven- 

 ger mud snails and, further up, a crowd of 

 Thysanura — small insects that rise to the 

 surface of the water when the tide comes in. 

 These find a living on the finer debris or 

 silt that settles on the pebbles during the 

 high tides. In this zone also Limulus lays 

 its eggs in the sand, and its nests are crowded 

 with nematodes that feed on the eggs. 

 During the breeding season scores of the 

 female Limulus die here, and their carcasses 

 determine a complex fauna. First, carrion 

 beetles {Necropliorus) and the flesh fly live 

 on the dead bodies ; then the robber flies 

 and tiger-beetles are here to feed on this 

 fauna, and finally numerous swallows course 

 back and forward gleahing from this rich 

 field. At the upper edge of the lower 

 beach is a band of debris dropped at slack 

 water and consisting especially of shreds of 

 Ulva and many drowned insects, chiefly 

 beetles. At this zone, or just above under 

 the drier but more abundant wreckage of 

 the last storm, occur numerous Amphipoda 

 of the genera Orchestia and Talorchestia. 

 Associated with these marine creatures are 

 numerous red ants, sand-colored spiders and 

 rove -beetles. The amphipods feed on the 

 decaying sea- weed. The ants are here look- 

 ing chiefly for the drowned insects. Their 

 nests are further up on the middle beach, 

 but the workers travel to the edge of the 

 high tide to bring away their booty. The 

 rove-beetles are general scavengers. The 

 spiders, which are mostly of the jumping 

 sort (of the family Atticke), feed on the ac- 

 tive insects and amphipods. At a higher 

 zone, and above all but the storm-driven 



tides, one finds the nests of the ants, espe- 

 cially under logs, certain predaceous beetles 

 and thexerophilous grasshoppers and crick- 

 ets. Finally, on the plant-covered upper 

 beach one finds characteristic leaf- eating 

 beetles, grasshoppers and carnivorous in- 

 sects. Now all this seems commonplace 

 enough and not especially instructive, and 

 yet if you go to the shore of Lake Michi- 

 gan you will find on a similar beach closely 

 similar, if not identical, forms (excepting 

 the beach fleas and the horseshoe crabs) you 

 will find similar ants, spiders, rove-beetles, 

 tiger beetles and sand-grasshoppers. This 

 fact alone shows the greater importance of 

 habitat over geographical region in deter- 

 mining the assemblage of animals that oc- 

 curs in any one place. It may be pre- 

 dicted that studies on the relation of animals 

 to their habitat will multiply, that they will 

 become comparative and that the science 

 of animal ecology will become recognized as • 

 no less worthy and no less scientific than 

 the science of morphology. 



Studies on the origin of species were far 

 from being unknown in the nineteenth cen- 

 tury, but they were for the most part frag- 

 mentary, or speculative, or narrow in view. 

 The opinion that there was one method of 

 evolution seemed to hold swsbj. It seems 

 to me that the signs of the times indicate 

 that we are about to enter upon a thorough, 

 many-sided, inductive study of this great 

 problem, and that there is a willingness to 

 admit that evolution has advanced in many 

 ways. The attempt, therefore, to explain all 

 specific peculiarities on the ground of nat- 

 ural selection, or on the ground of self-ad- 

 justment, or on the ground of sport preser- 

 vation through isolation, we may expect 

 equally to prove futile. All these causes 

 are no doubt real in some cases, but to ex- 

 clude any one or to deny that new causes 

 may be found in the future is equally dan- 

 gerous and unscientific. 



It is often said that the factors of evo- 



