ANIMAL AFFINITIES 



:89 



96. ON HOMOLOGIES AS INDICATIVE OF 



AFFINITIES 



Such a series of descents as is represented in the following 

 scheme may easily be observed : 



1 



8cc. 



Fig. 36. 



Here (case i) is an " ancestor," «o, which gives origin to the ova 

 that become the progeny a, and «2 '> ^i similarly gives origin by 

 reproduction to a^ and a^ and so on. All the organisms «o, ^1, «2) 

 etc., are adults and present the same assemblage of characters, 

 and these adult individuals are related together by the various 

 ontogenies, or individual developments, represented by the 

 oblique lines. 



Now these ontogenies are highly conservative processes : thus a 

 series such as the above one may extend to hundreds of millions 

 of terms. This is actually the case with the Brachiopods, Lingula, 

 which have existed without appreciable change since Cambrian 

 times. Transformism, however, must usually occur long before 

 a series extends so far and we may indicate such a change by the 

 diagram, 2 of Fig. 36. This means that at the stage represented 

 by a 3 transformism occurs and the individual, or individuals ^3 

 have produced ova that develop into individuals having characters 

 represented by ^0 and h^. That is, the developmental organization 

 has changed {wh.Qth.er hy " mutation," or " direct " or " somatic " 

 induction does not matter). Thus the series of developmental 

 phases, or the ontogeny a — a^, is not the same as the new onto- 

 geny a^ — bo which results from the change of developmental 

 organization. 



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