46 MANUAL OF ZOOLOGY. 



bably to be looked upon as, in some cases at any rate, the 

 embryonic, or larval, forms of the higher Infusoria which suc- 

 ceed 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 

 (Scolecida). It is therefore very unlikely that these should 

 be generated spontaneously ; since, if this ever occurs, it is 

 reasonable to suppose that the creatures thus produced will be 

 of the lowest possible organisation (such as the Gregarinidse 

 or the Monera, for example), and will be far below the Infu- 

 soria 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 main- 

 tained by the heterogenists, since this mode of reproduction 

 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 w r e 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 organic 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 Conferae ; 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 

 of the forms which are observed are the larval stages of the 

 higher Infusoria. 



h. Recent researches, especially those of Dr Bastian, have 

 established some new facts as to the possibility of spontaneous 

 generation, but they can by no means be said to have settled 

 the question, if only upon the ground that they require con- 

 firmation by other experimentalists. The chief fact which ap- 

 pears to have been established upon a tolerably firm basis is, 

 that living beings, vegetable or animal, may make their ap- 

 pearance in organic infusions which have been subjected to a 

 temperature of considerably over the boiling-point, even though 

 the said infusions have been hermetically sealed in a flask from 

 which all atmospheric air has been previously withdrawn. The 



