iNFrsoKiA. 53 



CHAPTER VII. 



IXFUSORIA. 



I. Nature of Infusoria. — 2. Example of the group : Vorticella 



3. Classification. — 4. Size. — 5. Form and Structure. — 6. Diges- 

 tive apparatus. — 7. Contractile vesicle. — 8. Nucleus, &c. — 

 9. Urticating organs. — 10. Locomotive organs. — 11. Develop- 

 ment. — 12. Distribution. — 13. Noctiluca. 



I. IVature of Isafiisoria. — If water, in con- 

 tact with organic matter, be exposed to the atmo- 

 sphere for a few days, it will probably be found to 

 contain, upon examination, a considerable number 

 and variety of living beings, whose size is such as 

 to render the majority of them invisible to the 

 unassisted eye. These minute creatures received 

 from the older microscopists the name of Infuso- 

 ria, a term having reference to their frequent oc- 

 currence in most animal and vegetable infusions. 

 Subsequently, they were investigated with great 

 industry by Ehrenberg, who figured and described 

 a vast number of " species " belonging to the 

 group, all of which he arranged under two leading 

 divisions, denominated respectively, Rotifera and 

 Polygastrica. But the recent observations of se- 

 veral eminent naturalists have, however, shown 



1st, That the organisation of the Rotifera is of 

 a far higher nature than had been suspected 

 by Ehrenberg, and that the true position of 

 these animals is in the Annuiose sub-kinofdom* 

 and, 



2ndly, That the Polygastrica of Ehrenberg may 

 be defined as a heterogeneous assemblage of 



E 3 



