VI TREFACE. 



were finished, that the arrangement of Dr. E.'s figures 

 did not agree with his text : thus, even species are some- 

 times 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. 



In conclusion, the labour and cost of this undertaking 

 has far exceeded my anticipation ; but should it meet with 

 patronage sufficient to repay the outlay, and my health 

 permit, it is my intention to bring out, on another branch 

 of Microscopic Science, a work of equal extent to the 

 present, materials for which I have been for some time 

 collecting. 



London, 162, Fleet-streel ; 

 \8fh March, 1841. 



Postscript. — Since the above was written. Dr. Ehreu- 

 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, 184L 



