GROUNDS AND CONSEQUENCES OP EVOLUTION. 347 



stimulated by the nutritive plasma in which they are 

 bathed. Generative or genealogical development begins 

 in the multiplication and specialization of a cell stimulated 

 by contact with a cell specialized sperm atically in the 

 same individual or in an individual sexually different. 

 Propagation, moreover, may be viewed as simply a mode 

 of perpetuating or renewing an individual which is bisexual, 

 either monoeciouely, as in lower animals and most plants, 

 or dioeciously, as in most animals and certain plants. The 

 progress noted in the succession of extinct forms is assumed 

 to have resulted from some influence exerted upon embryos 

 in the progress of their development. The development 

 accelerated or prolonged would end in an organism more 

 advanced. This would be a new specific form appearing 

 as a stage of embryonic history; and though many gen- 

 erations may have intervened while the embryo was arriv- 

 ing at this new specific type, we may view these genera- 

 tions as simply nature's expedient to continue the being 

 in existence in spite of the wastes of physical life. So 

 what seems at first a mere analogy resolves itself into a 

 profound biological identity. 



To sum. up, we have, it appears, an identical order of 

 succession of organic forms three times repeated. The 

 first appears in the successive transformations of the indi- 

 vidual being before it reaches maturity. This succession 

 is ontogenetic and rapid. It is repeated for every individual 

 which comes to maturity. The second succession is pre- 

 sented in the geological history of extinct life. It is not 

 yet observed to be parallel in all details, but the progress 

 of discovery tends continually to complete the parallel. 

 This succession is palceontological and slow. The third 

 succession is presented by the serial order of living ani- 



