532 THE KEPKODUCTIVE FUNCTIONS. 



In the instances which have now passed under 

 our review, the progeny is, at first, in direct com- 

 munication with its parent, and does not receive 

 the special protection of membranous envelopes, 

 containing a store of nourishment for its subsequent 

 growth. But in all the more perfect structures, 



diligent observer detected the young of the Rotifer vulgaris, per- 

 fectly formed, moving in the interior of the parent animalcule, and 

 excluded in a living state ; thus constituting them viviparous ani- 

 mals, as the former were oviparous. Other species, again, imitate 

 the hydra, in being what is termed gemmiparous, that is, producing 

 gemmules (like the budding of a plant), which shoot forth from the 

 side of the parent, and are soon provided with cilia, enabling them, 

 when separated, to provide for their own subsistence ; although they 

 are of a very diminutive size when thus cast otf. 



Some of the German naturalists go much farther than Buffon ; 

 and profess their belief that organized beings may be produced out 

 of an assemblage of perfectly inorganic materials ; such as the 

 earths, when mixed with pure water, to which atmospheric air has 

 access, under a certain temperature; or, in other words, by the con- 

 current but exclusive agency of the four elements of the ancients. 

 There is, however, little doubt that in all these cases, invisible germs 

 were introduced through the medium of the air in which they are con- 

 stantly floating : for when sufficient care is taken to exclude them, 

 no organic beings make their appearance. This has been satisfac- 

 torily shown by the negative result of an experiment recently made by 

 F. Schultze, of Berlin, who placed various organic materials in a 

 flask with water, the mixture being kept boiling for some time so as 

 to destroy the vitaHty of all the germs that might have been present; 

 and bent tubes being then adapted so as to allow no air to be ad- 

 mitted, except such as had passed either through sulphuric acid on 

 the one side, or a solution of potass on the other. The vessel was 

 allowed to remain in this state for above two months, during the 

 whole of which time, neither confervae, infusoria, nor any other 

 organic being could be discovered in any part of the contents of the 

 vessel : while in another vessel, containing the same materials, but to 

 which the air had free access, they made their appearance in great 

 numbers in the course of a few days. Edin. Phil. Journal, xxiii, 

 165. 



