x.] BIOGENESIS AND ABIOGENESIS. 239 



were given me to look beyond the abyss of geologically 

 recorded time to the still more remote period when the 

 earth was passing through physical and chemical con- 

 ditions, which it can no more see again than a man can 

 recall his infancy, I should expect to be a witness of the 

 evolution of living protoplasm from not living matter. 

 I should expect to see it appear under forms of great 

 simplicity, endowed, Hke 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 analogical 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 Kedi'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 Kedi, 

 whether Xenogenesis obtains, side by side with Homo- 

 genesis, 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 dif- 

 ferent 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 substance of these plants, was 

 made out by Vallisnieri, Eeaumur, and others, before the 

 end of the first half of the eighteenth century. The 

 tapeworms, bladderworms, and flukes continued to be 

 a stronghold of the advocates of Xenogenesis for a 

 much longer period. Indeed, it is only within the 



