PREFACE. xi 



whereby they are converted into the embryos of 

 large and complex Rotifers. 



Visible phenomena of Synthetic Heterogenesis thus 

 serve, as it were., to demonstrate the mode in which, 

 by invisible processes, the simplest living units may 

 arise. So that after watching all the steps of the more 

 complex phenomena, we may find it less difficult than 

 we should otherwise have done to believe in the occur- 

 rence of the simpler process of Archebiosis more espe- 

 cially when its occurrence is attested by facts and 

 probabilities of the highest independent value. 



Again, we know that simple mineral substances may 

 exist in different allotropic conditions, just as numeri- 

 cally-similar combinations of different elements may 

 exist in two or more isomeric states. But, if mere 

 differences in molecular arrangement may cause sulphur 

 or arsenic, on different occasions, to present wholly 

 different appearances and properties j or if a similar 

 alteration in molecular arrangement may lead such salts 

 as mercuric iodide to pass easily from one to another 

 mode of crystallization, it should not be very difficult 

 for us to believe that living matter might also, with 

 comparative ease, undergo somewhat analogous mole- 

 cular rearrangements, and that such changes might 

 also entail some modifications in the form and other 

 attributes of the living aggregate. And now, as matter 

 of fact, we have to state that the occurrence of Hetero- 

 genetic Transformations amongst lower living things 

 and in portions of higher living things have been 

 almost as well attested as the occurrence of allotropic 

 and isomeric modifications amongst different kinds of 

 not-living matter. 



