THE BEGINNINGS OF IIFE. 



309 



changes to occur in various parts of the body when the 

 general ^ vital powers' are lowered by disease 1. And, 

 for a similar reason, heterogenetic changes take place 

 still more freely when the organism itself is dead, 

 and when its component parts are left to struggle on 

 under the most adverse circumstances, until the little- 

 remote period when death overtakes them also-. 

 Then in all parts of the dead organism there is a 

 bursting-forth into new life. Myriads of Bacteria and 

 Fungus - germs are born from their parent fluids, 

 though all this is hidden from our ordinary view, and 

 its effects only become manifest when the ever-varying 

 forms of ^ mould' and '^mildew' appear and flourish on 

 the surface of the previously living aggregate ^. 



For the most part I intend to confine myself to the 

 consideration of the mode of origin of these lowest 

 organisms within the substance of higher plants and 

 animals. I do not propose to enter into the question 

 of the possibility of the independent origin of any of 

 the higher parasitic Entozoa. The occurrence of these 

 parasites was formerly regarded as one of the strongest 

 points in favour of the doctrine of Heterogeny. But 

 the investigations of numerous helminthologists have 

 done much to remove very many of the difficulties 

 which were formerly regarded by Miiller and others as 

 almost impossible to be explained on the supposition 



^ See p. 190. 2 ggg yol. i. p. no. 



3 See Prof. Grant's ' Tabular View, &c., of Recent Zoology,' pp. 5 

 and 91. 



