THE ORIGIN AXD THE EXTIXCTIOX UF -PECIE? 355 



of species t-j viuy }>ei-sisreutly onwards, and to ■ become fiu-ther anl 

 fvu-ther removed fi-om the primitive tvpe. as lias been maintained, 

 then such ancient and primitive Cephalopod forms like the Xautihu- 

 species could not have persiste*.! imtil now, but must long ago have 

 l;>een transmuted into higher forms. The convei-se. however, is con- 

 ceivable enotigh. namely, that the gieat mass of the species of a group 

 such as the Xauiilida? were crowded out by --tiperior rivals in the 

 -tiTiggle for existence, but that cenain species were able to sur\-ive 

 on .specially pi-otected or cahei-wise favoured areas. We have a fine 

 example of this in the few stiU living species of the otherwise 

 extinct da-s^^ of Ganoid fishes. During the Primary and Seccndaiy 

 epochs these Ganoids pec^ple-l all the seas, but at the boundary 

 Wtween the Cretacec'us and the Tertiarj- period they retrjgi-ade<i 

 considerably, simtdtane-aisly with the great development cf lony 

 fishes or TeleC'Steans. and now they are only represented by a dozen 

 species distribute<l over the earth, and most of these are purely river 

 forms, while the othei-s at least ascend the rivers dturing the spawning 

 seas-jn to secure the safety of their progeny. For the rivers are 

 sheltered areas as c-ompared w-ith the sea^?. and large fishes like the 

 Ganoids will be able there to hold their own in the st:iig^-le l>etter 

 than they cotdd in the incomparably more abundantly peopled sea. 



Thus I can only regard it as playing with ideas to speak of birth, 

 blossoming, standstill, decay, and death of species in any other than 

 a figurarive sense. T7ndoubte<ily the life of the sj^eeies may V-e 

 compared with that of the individtial. and if the comparisiDn he used 

 only to make clear the difference between the causes of the two kinds 

 of phenomena, there can be no oljecrion to it. only we must beware 

 of thinking ^we have explained anything we do not know ty c-ompaiiu ^- 

 it with smner hiri g else that is also unknown. 



We have alrea-ly shown that the natural death of multicellular 

 organisms is a phenomenon ^vhich first made its appearanc-e with the 

 separation of the org anis m into s-jmatic or l-ixiy cells and reproiiuctive 

 or germ c-ells. and that death is not an inevitable Xemesis of every hfe. 

 for unicellular ori^ranisms do not necessarily die, though fhey may 

 be killed by virlenoe. These unicellular oiganisms have thus no 

 natural death, and we have to explain its occurrence among nmlti- 

 cellular organisms as an adaptation to the cellular ■iilferentiation, 

 which makes the tmlimited continuance of the life of the whole 

 organism unnecessarv and purposeless, and even prejudicial to thr- 

 continuanc-e of the species- For the species it is enough if the germ- 

 cells alone retain the potential immortality of the unieellulars, while, 

 on the other hand, the high dilferenriation of the somatic cells neces- 



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