SPONTANEOUS GENERATION. 39 



themselves out of the inorganic materials of the infusion ; since 

 this implies the sudden appearance, or creation, of new force, 

 for which there seems to be no means of accounting. 



b. The nature of the vibrios and bacteria must be looked 

 upon as quite uncertain. To say the least of it, they are quite 

 as likely to be plants as animals ; and the most probable hypo- 

 thesis would place the former near the filamentous Confervse, 

 or would regard them as the mycelium of various species of 

 Moulds (PtnidUium). 



c. What has been said above with regard to the origin of 

 the bacteria and vibrios applies equally to the origin of the 

 Monads, which appear in the infusion subsequently to the 

 death of the vibrios. 



d. These Monads, as shown by recent researches, are pro- 

 bably to be looked upon as the embryonic, or larval, forms of 

 the higher Infusoria which succeed them. 



e. Many of the Infusoria which finally appear are of a 

 comparatively high grade of organisation, being certainly the 

 highest of the Protozoa, and being placed by some competent 

 observers in the neighbourhood of the Trematode Worms 

 (Annuloida). It is therefore very unlikely that these should be 

 generated spontaneously ; since, if this ever occurs, it is reason- 

 able to suppose that the creatures thus produced will be of the 

 lowest possible organisation (such as the Gregarinidae or the 

 Monera, for example), and will be far below the Infusoria in 

 point of structure. 



f. The reproductive process in many of these same Infusoria is 

 perfectly well known, and it consists either in a true sexual 

 process, for which proper organs are provided (as in Paramce- 

 cium), or in a process of gemmation or fission. It is therefore 

 improbable that they should be generated in the manner 

 maintained by the heterogenists, since this mode of reproduc- 

 tion would appear to be superfluous. 



g. In the absence of any direct proof to the contrary, it is 

 safer to adopt an explanation of the observed phenomena 

 which does not have recourse to laws with which we are as yet 

 unacquainted. Thus, it is not at variance with any known law 

 to suppose that the primary molecules are the result of the 

 development of germs which find in the inorganic infusion a 

 suitable nidus ; that these primary molecules and the vibrios 

 which they produce are referable to the Protophyta, and should 

 probably be placed near the filamentous Confervae ; that by 

 the death of these vegetable organisms the fluid is prepared 

 for the reception and development of the germs of the Pro- 

 tozoa, for which the former serve as pabulum ; and that many 



