APPENDIX. 99 



of such cells, and this structure be so attenuated 

 and infinitesimal as to elude observation ; or whe- 

 ther it results from the transmission of some peculiar 

 modification of that mysterious vital force we term 

 nervous influence, are questions, to which, in the pre- 

 sent state of our knowledge, no satisfactory reply can 

 be given. 



Localities of Fresh-water Infusoria, p. 28. — The fol- 

 lowing remarks on the situations in which the differ- 

 ent kinds of fresh-water animalcules may generally be 

 found, offer some useful suggestions to the inexpe- 

 rienced observer*. 



In stagnant and putrid water, the ordinary forms of 

 Infusoria only are met with ; but in clear pools and 

 streams the most elegant species abound, and are often 

 found clustering around, or attached to the stems and 

 under-sides of the leaves of aquatic plants. Twigs, 

 leaves, &c., that are beneath the surface of the water, 

 particularly such as appear to be coated with slime, 

 will be found to harbour myriads of Vorticellas, Roti- 

 fers, &c. The yellow, green, blue, reddish, and brown 

 mucus floating on the surface, generally swarms with 

 interesting and beautiful species. 



* Translated from Mandl's ** Traite pratique du Microscope." 



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