The Natural History of the Animalcules. 
By the Editor. 
HE question naturally arises at the very threshold, 
11 what are Animalcules ?'• and many very 
pra6lical natures, to whom the cut bono is the 
beginning and the end, without waiting for an answer 
which might throw some light upon the question, will 
doubtless pass at once from the simple " what are they ?" 
to the uncompromising " of what good are they ?" with 
the evident desire that the justification of the subjeft 
itself on the ground of utility should be stated, as a first 
and necessary preliminary to their attention and interest. 
At the outset it must be pointed out that, in an essen- 
tially popular account of these organisms, only partial 
and inadequate answers can be given to these two 
questions, since their wide bearing and importance 
would only be evidenced as the Animalcules themselves 
passed in review, and yielded the knowledge necessary 
for the thorough comprehension of their stru6lure and 
life history. 
In a stri6l use of the term, Animalcules should refer 
only to the most minute members of the animal king- 
dom — >to those, in fa6l, which are, or almost are, beyond 
the reach of ordinary vision, and which, as a rule, require 
a magnifying-glass or microscope for their dete6lioii. A 
microscope is in every case necessary for the study of 
their structure ; and while by this means many are known 
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