Prof'. Ehi-enherg's Researches on the Infusoria. 79 



of the animal kingdom. When the microscope received no aid 

 in the unravelHng of their structure from the use of coloured 

 substances or other artificial means, their apparently homoge- 

 neous tissues furnished no distinctive characters, except the va- 

 rieties of external form, the presence or absence of ciliae and 

 other appendages, which are so uncertain and so changeable, 

 and which have been long ago rejected from other departments 

 of zoology as the fundamental bases of division. Upon this 

 basis rest the systems of Miiller, of Bory St Vincent, and of all 

 other systematologists. Cuvier, in the last edition of the Regiie 

 Anijnal, has endeavoured in vain to reduce into a connected 

 system a few isolated observations of more importance on some 

 individuals of the class, furnished by Dutrochet. 



It is now necessary to reduce these animals to the general 

 rules of zoology, and to form a " distribution according to their 

 organization." Dr Ehrenberg cannot be accused of precipi- 

 tancy in erecting a new system upon his own observations, 

 which have not of course extended to all the species already de- 

 scribed by naturalists ; but by numerous microscopic observar. 

 tions pursued night and day with indefatigable industry, he has 

 been enabled to reduce all the principal forms to fixed princi- 

 ples, upon which he has constructed the two following tables, 

 which remain to be increased by future observations, but of 

 themselves will, at first sight, be seen to form an immense ac- 

 cession to the domain of natural history. 



It will be requisite, however, in the first place, to make a few 

 observations upon the principles which have guided him in their 

 construction. He has included under his categories those ge- 

 nera or species onli/ whose digestive organs he has demonstrated 

 himself by his new method of observation. Many other species 

 which he has examined, but whose organization has not been 

 subjected to this scrutiny, as well as some genera which either 

 oppose his system, or regarding whose structure we are quite 

 ignorant, he has classed in an appendix under the heads to 

 which they probably belong. 



He has rejected from the Infusoria the genera Cercaria, 

 Nitsch, Spermatozoon, Baer, and the Vibrio JIuviatiUs and aceti 

 Miiller, to which he has given the generic name of AnguUlida. 



