1 82 THE BEGINNINGS OF LIFE. 



These quotations will suffice to show the amount 

 of favour with which doctrines of heterogeny were 

 regarded by many of our predecessors, and also to 

 indicate the nature of some of the problems which 

 remain to be investigated. 



It will be found, however, that the facts which we 

 have to consider may be ranged under two distinct 

 categories. We have to study processes that may be 

 classed under the head of Synthetic Heterogenesis, 

 and others belonging to what may be called Analytic 

 Heterogenesis. The latter set of changes may, for the 

 sake of convenience, be studied under two heads : 



1. Synthetic Heterogenesis refers to the origin of larger 



and somewhat more complex forms of life, by a 

 process of fusion, with molecular re-arrangement, 

 taking place amongst the simplest living units. 



2. Analytic Heterogenesis refers to the origin and pre- 



sence of some of the simplest forms of life from 

 and within the bodies 'of other organisms: 



a. Within the bodies of higher animals and plants. 



y. Within the substance of lower organisms, both 

 animal, protistic, and vegetal. 



croire que la raison de leur apparition est absoluement sous 1'influence 

 des affinites ; ce serait rabaisser la creation au niveau d'uue attraction 

 chimique. Non, la cause intime de la vie, cette force initiale qui en 

 groupe le canevas est cet esprit que Bremser considkre comme le regu- 

 lateur de tous les actes biologiques.' In fact, M. Pouchet definitely pro- 

 fesses to be a ' vitalist,' and says (p. 428), ' I have always thought that 

 organized beings were animated by forces which are in no way reducible 

 to physical and chemical forces.' 



