PREFACE. Vll 



venerable and distinguished botanist, Dr. Unger, of Gratz, 

 and the late eminent microscopic observer, Mr. F. Bauer. 

 Every original drawing has the artist's name mentioned in 

 the description of it, and the others, with few alterations, 

 are from Die Infusionsthierchen. The labour and time 

 occupied in selecting, reducing, arranging, and condensing 

 these, was far greater than most persons would imagine, 

 and has been augmented by the discovery, after some were 

 finished, that the arrangement of Dr. E/s figures 'did not 

 agree with his text : thus, even species are sometimes 

 widely separated, and creatures figured under one name 

 are described under another; so that, in some cases, the 

 drawings had to be made three times. 



London, 162, Fleet-street; 

 ISth March, 1841. 



POSTSCRIPT. Since the above was written, Dr. Ehren- 

 berg's work on Infusoria found in the Chalk Formations, 

 published at Berlin, has appeared ; and, in order to bring 

 the subject down to the present time, I have inserted an 

 abstract of it in an Appendix. 



June, 1841. 



