THE BEGINNINGS OF IIFE. 259 



new made, and boasting of no line of ancestors — are 

 the products of the very conditions and matter in and 

 from which they are produced, and are therefore liable 

 to present endless minor modifications on different 

 occasions. 



We can confidently appeal to those who have care- 

 fully studied the organic forms which teem in infusions, 

 to bear us out in the assertion that they do exhibit 

 all this diversity which, owing to their nature and 

 mode of origin, we have been supposing they ought to 

 present. We have already spoken of the extreme 

 diversity amongst the primary organic forms — such as 

 Bacteria^ ToruU^ and their allies; and with regard to 

 the lowest microscopic Fungi and the lowest micro- 

 scopic Algse, their inconstancy of specific form is most 

 proverbial \ Similarly, the extreme variability of the 

 Ciliated Infusoria was well known and commonly noted 

 even by the older naturalists, whether they were be- 

 lievers in specific identity or not. 



Both Gruithuisen^ and Treviranus^ say that the in- 

 fusoria met with have never presented similar charac- 

 ters when they have been encountered in different 

 infusions; nor have they been more uniform in the 

 same infusion when different portions of it have been 

 exposed to the incidence of different conditions. The 

 slightest variations in the quantity or quality of the 



^ See Appendix E, pp. Ixix and Ixxvi. 



2 * Organozoonomie,' p. 164. Munich, 1811. 



3 See Miiller's ' Physiology,' translated by Baly, pp. 12 and 13. 



S 2 



