VIII BIOGENESIS AND ABIOGENESIS 257 



forms of great simplicity, endowed, like existing 

 fungi, with the power of determining the formation 

 of new protoplasm from such matters as ammonium 

 carbonates, oxalates and tartrates, alkaline and 

 earthy phosphates, and water, without the aid of 

 light. That is the expectation to which analogi- 

 cal reasoning leads me ; but I beg you once more 

 to recollect that I have no right to call my 

 opinion anything but an act of philosophical 

 faith. 



So much for the history of the progress of 

 Redi's great doctrine of Biogenesis, which appears 

 to me, with the limitations I have expressed, to 

 be victorious along the whole line at the present 

 day. 



As regards the second problem offered to us by 

 Redi, whether Xenogenesis obtains, side by side 

 with Homogenesis, whether, that is, there exist 

 not only the ordinary living things, giving rise to 

 offspring which run through the same cycle as 

 themselves, but also others, producing offspring 

 which are of a totally different character from 

 themselves, the researches of two centuries have 

 led to a different result. That the grubs found 

 in galls are no product of the plants on 

 which the galls grow, but are the result of the 

 introduction of the eggs of insects into the sub- 

 stance of these plants, was made out by Vallisnieri, 

 Reaumur, and others, before the end of the first 

 half of the eighteenth century. The tapeworms, 

 M 



