VI PREFACE. 



benefit would accrue to science by reconstructing it, and 

 introducing the discoveries made since that time, than by 

 a mere reprint. 



Dr. Ehrenberg's magnificent and elaborate work, entitled 

 Die Infusionsthierchen, having since appeared, and offering 

 a better classification than Muller's, it has been adopted 

 here. I have only to regret that its distinguished Author, 

 or some more competent Naturalist than myself, has not 

 presented us with an epitome of it. 



In the description of the families, genera, and species, 

 I have not adhered to Die Infusionsthierchen, but only 

 condensed such portions as appeared desirable, interweav- 

 ing them with other matter : hence it would be unjust to 

 its Author to consider this manual an abstract of it. That 

 work being intended to establish a new classification, and 

 as a book of reference, a large portion of its ample 600 

 folio pages is occupied in giving the synonyms, in 

 references, and in discussions; these I have omitted, but 

 every species described in that work will be found here, 

 together with many others since discovered. 



A new system of classification is seldom acceded to 

 wholly at first : that by Dr. Ehrenberg has met with its 

 share of opponents. The principal arguments respecting it 

 will be found herein ; so that the student, having both 

 sides of the question before him, will be able to arrive at a 

 fair conclusion. 



A few words seems necessary regarding the drawings. 

 Those for plate xii. were kindly furnished me by that 



