INFUSORIAL ANIMALCULES. 23 



the Infusoria: 1. They have no oral aperture. 2. They 

 never propagate by direct self- division, but by the mere 

 dissolution of the gemmee. 3. They increase in size only 

 by the growth of the gemmee. 4. They have both the 

 external and internal rigidity of vegetable organization. 

 5. The impregnation of the Spyrogyra resembles that 

 of some of the species of Fungi. 6. They develope 

 acicular crystals within themselves, like some well-known 

 plants. 7 Their motion is not perceptibly voluntary. 

 For further particulars, see remarks on the Closterium, 

 Part II. 



Spontaneous Generation. Many of my readers may 

 expect to find some notice of this subject, as the Infusoria 

 are considered to have a generatio primitiva, or, in other 

 words, are produced by some fortuitous combination of 

 circumstances from inorganic matter. That such a state- 

 ment is untenable, most persons will be inclined to admit, 

 who have perused the description contained in the Second 

 Part of this work. All the observations that can be 

 depended upon tend to show that infusions of vegetable or 

 animal matters, whether natural or artificial, only offer 

 food for the nourishment of these living atoms, whose 

 germs are almost everywhere present, but are only de- 

 veloped in situations congenial to their natures. It is now 

 well ascertained that the old notions of certain vegetable 

 infusions producing a definite species of Infusoria is an 

 error ; that, in general, we have, in all artificial infusions, 

 only common species, and that these invariably making 

 their appearance, we may fairly presume their eggs are 

 more generally dispersed and more readily developed. 

 On the other hand, the Rotatoria, and more beautiful 



