6 14 THE BEGINNINGS OF LIFE. 



life (including the Foraminifera) which were to be found 

 in such situations at that time had been produced by 

 Archebiosis combined with Heterogenesis ; so that if 

 the conditions have been always so similar in the 

 regions in question, we might expect that more or less 

 similar forms would have been constantly arising by 

 Archebiosis and Heterogenesis, and that these would 

 also go through comparatively similar developmental 

 changes. 



The theory of c lineal descent ' is most unlikely to be 

 true; because, as we have already pointed out, the 

 improbability is extreme that such low and unspecial- 

 ized forms should have existed through so many ages 

 without undergoing any appreciable advance in com- 

 plexity of organization. On the other hand, many of 

 the ordinary forms of Foraminifera may have been 

 produced originally, as well as in all subsequent periods, 

 by the occurrence of comparatively common hetero- 

 genetic changes : and such a view is all the more easy 

 for us to adopt now that we know how readily Arcellinae 

 are still engendered from the substance of dying Roti- 

 fers and other low organisms \ 



Almost similar modes of reasoning are, moreover, 

 now applicable in order to explain the existence 

 through successive geological epochs of many other 

 lower forms of life. Concerning the facts, Prof. 

 Huxley says 2 : c Certain well-marked forms of living 

 beings have existed through enormous epochs, sur- 



1 See p. 486. 2 'Proc. of Roy. Instit.,' vol. iii. p. 151. 



