THE ORIGIN ANP THE EXTIXi riON OP ?rKOIES 353 



or etonial, but that thov eliaagv^ in the eoui-so of the earth's liistt^ry. 

 The nvimeivus fo^il ivmaius in the various strata of tlio e^utlts crust 

 piv\-e that this is true in a high doiriw. tliat in ahuost every oue of 

 the u»oiv i»u^x>rtant jjixilogieal strata new speoios oe?\ir. and that not 

 only sjxx'ies and ofenei-a, but families, or^iei-s, iudeevi whole classes of 

 animals, which liA'eil at one time, have now completely di.sappeai"ed 

 fi\>m the fact^ of the earth. Wo can understand this phenomenon 

 when we tvtl^x't that the conditions of life have also been slowly 

 chatij^ing- thivuofh the Cvnii^c of the eaith's history, so that the 

 old sj.veies had only the alteniative of dying out. or of Ivecomiug 

 transformed into new sp^vics, 



Btit simple as this conclusion is. it can hai\ily lie deduced with 

 certainty fivju the ^xxnirrence and suci>ossiou of the f^vssil species 

 alone. For instance, we sliould strive in \"ain to recognize the catise 

 which led one of those rci:u';uly arranortxl siuail-sjvcies of the 

 SuinV.o-;n lake basin to l^ecome traustoruied into one or two new 

 species at a pirticnlar time, or to find the cause which moved those 

 curious tripartite Crusta^vans of primitive times, the Tiilobite*. which 

 peviph>l the S.air;;v.i seas with such a wealth of tonus, to become 

 suddenly seaw^e towanls the end of the Sr.\;r:;'.!\ perio^l. and to dis- 

 appear a'.together in the succeetiing period, the Devonian. The 

 famous gev^logist NenmaxT sought to refer this strikiiig phenomenon 

 to the fact that jxist at that time the Cephalopols, ■ the most formid- 

 able and Siiv^agv mai-audcKt among the invertebrate marine fauna.' 

 gained the ascendancy, and it is quite po,ssible that he was right 

 in his svirmis<\ but who is to piwe it ? Can we decide even in the 

 case of animals now living whether the h\ssos inflicted on a much 

 persecutetl sp^vios by an abundant and gi-eedy jvi^ecutor exceed the 

 nnmbei-s of pK>p:niy. and ai^ thervfoi-e driving the s}^«acs gradvially 

 towarvls extermination ? Probable as such a supposition appeaIS^ it 

 cannot be accepted as proven. 



Sir.oe in m.any cases of the extinction of giieat animal-groups we 

 cannot even pixne that theiv was a simultaneous ascendancy of power- 

 ful enemies, other factoi~s must W discv^ver^ed to which the apparently 

 sudden disappearance may be attributeil. Many natni-alists have 

 tried to i^uoss at internal iw^sons for extinction, and have adopte^l the 

 theory — ass^^iciated with the tendency to assume mystical principles of 

 evolution — that species in dying out ane obe\-ing an internal necessity, 

 as if their birth and death wei'* ptvdestined. as it is in i;.e case of 

 mnHacellnlar individuals, as if ther^ wer>e a /ifty!f»ofotir«*w/ death o?" f Se 

 -s/ift"sVs as theiv is of the muMcellnlar indi^^duaL 



Xevmiayr showeil, however, that the facts of palawntoIog\- affiuxi 

 II. Aa 



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