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Genus MONAS Muller, 1773. 
This genus was originally published with the diagnosis: “Vermis 
inconspicuus, simplicissimus, pellucidus, punctiformis,” to contain the 
three species Monas termo , M. lens , and 2L mica . It is needless to 
say that with the technique of 1773 these species are not described 
with the minuteness that we expect to find in descriptions published 
at the present day, and if they are judged from the standards of 1905 
instead of 1773, authors will doubtless admit that they may be applied 
to so many species that it is uncertain just which particular form 
Muller studied. If, however, this principle were applied generally to 
zoology and botany, we should be obliged to make a new start in 
nomenclature every few decades. The proper method to follow in a 
case of this kind is an historical stud}" of the literature and synonymy, 
judging the subject from the successive standards as these improved, 
. and accepting as correct the assertions of successive authors that they 
have recognized the older species, unless we are in a position to prove 
their assertions incorrect. The result of such a study is that early 
species are gradually narrowed down to closer limits until they become 
restricted to forms recognizable on basis of our present standards. 
In the case at hand the history of the three species in question, so far 
as literature is at my command, is as follows: 
1. Monas termo Muller, 1773, 25-26. Ehrenberg, 1830a, 57, 81, etc., 1832c, 57, 
claims to have recognized this same species, adopting the name Monas termo Muller, 
but later authors (Dujardin, 1841a, 212; Diesing, 1850a, 16, 28) consider Ehrenberg’s 
form distinct. Ehrenberg, 1832c, 70, also mentions a “ Bacterium f termo .” 
Dujardin, 1841a, 212, transferred “ Monas termo Muller, non Ehrenberg” to Bac- 
terium as Bacterium termo (Muller) Dujardin, and the species is retained here in 
Diesing, 1850a, 16. 
Migula, 1897, 2, states that Monas termo Muller can with some certainty be 
viewed as belonging to the bacteria; Cohn (1872, 168) accepts Bacterium termo (as 
limited by Dujardin) as one of the two species of the genus Bacterium , as emended 
by him. 
2. Monas lens Muller, 1773, 26-27. Retained in Monas by Dujardin, 1841a, 280; 
placed in subgenus Mastichemonas by Diesing, 1850a, 32. Migula, 1897, 2, thinks this 
species belongs to the bacteria. 
3. Monas mica Muller, 1773, 27. Retained in Eumonas (typical subgenus of Monas ) 
by Diesing, 1850a, 25. This species is thus seen to be type of the genus Monas , by 
elimination, and as limited by Diesing, 1850a. 
Genus BACTERIUM Ehrenberg, 1828. 
[Not Bactiria Eisch., 1811, echinoderm; not Bacteria Latreille, 1825, orthopteron; 
not Bacteria for Bactiria, 1811.] 
1828: Bacterium Ehrenberg in Hemprich & Ehrenberg, 1828; Ehrenberg, 1830a, 58. 
The use of Bactiria , 1811, and Bacteria , 1825, does not necessarily 
invalidate Bacterium , 1828. 
The genus Bacterium was first proposed by Ehrenberg in a paper 
presented before the Academy of Science, Berlin, Germany, on Janu- 
