C. Dobell 
181 
those who would look for it. For it is evidently uncommon, it occurs in an 
unknown organ of a host whose species can only be guessed 1 , and it can only 
be known, when found, by its resemblance to Schneider’s imperfect figures. 
Labbe (1893), accepting Isospora as a form possessing two polyzoic spores, 
introduced the new generic name Diplospora for a coccidial parasite which he 
had found in birds, and which possessed two tetrazoic spores. In his sub¬ 
sequent works (Labbe, 1896 and 1899) he adhered to this nomenclature : but 
other workers have considered that Diplospora is a synonym of Isos'pora, 
believing Isospora rara to have been also a coccidium possessing two tetrazoic 
spores. This is the view generally taken, and it has the support of such 
authorities as Laveran and Mesnil (1902) and Schaudinn (1900). On the other 
hand Leger (1911), a great authority on the Coccidia, still prefers to regard 
Isospora and Diplospora as separate genera, believing that so accurate an 
observer as Schneider could not have mistaken a tetrazoic for a polyzoic spore. 
Minchin (1903, p. 232, footnote) has expressed the same opinion. 
For my own part I am disposed to assume the standpoint of Laveran and 
Mesnil (1902) and to regard Diplospora Labbe as a synonym of Isospora 
Schneider; and I shall follow them, and the majority of recent authors, in 
referring the coccidia which produce oocysts containing two tetrazoic spores 
to the genus Isospora. The two best known species of this genus, though 
neither can be regarded as the type, are the forms generally called I. bigemina, 
from the intestines of cats and dogs, and I. lieberkuhni from the kidney of the 
frog 2 . The human parasite which I shall refer to this genus—following Wenyon 
(1915)—bears the closest resemblance to I. bigemina, with which, as we have 
already seen, it has frequently been confounded. 
The coccidial parasites of man can thus be referred to their genera, accord¬ 
ing to the characters furnished by their oocysts and spores, in the following wav: 
Genus 1. Isospora Aime Schneider, 1881. (= Diplospora Labbe, 1893.) 
Oocyst containing two tetrazoic spores. 
Genus 2. Eimeria Aime Schneider, 1875. (= Coccidium Leuckart, 1879.) 
Oocyst containing four dizoic spores. 
1 It is sometimes stated that Isospora rara occurs in the kidney, and that its host is Limax 
cinereo-niger (cf. Doflein, 1911): but these are mere guesses—plausible, no doubt, but still quite 
unverified. 
2 I have already had occasion to note on a previous page that the correct name of “ Isospora 
bigemina Stiles, 1891,” is probably I. rivoltae Grassi, 1879. The parasite of the frog was first found 
by Lieberkiihn in 1854 but not named by him. Labbe named it Klossia lieberkuhni (in 1894) and 
later Hyaloklossia lieberkuhni (1896, 1899). Laveran and Mesnil (1902) regarded Hyaloklossia as 
a synonym of Isospora, and therefore called the parasite Isospora lieberkuhni Labbe, a name which 
it has since borne. It appears to have been overlooked, however, that the parasite was possibly 
first named by Rivolta (1878), who called it Cytospermium ranae. Its correct name therefore 
would be Isospora ranae Rivolta, 1878. I may also note here that it is possible to regard 
Cytospermium as the “correct” name of the genus here called Isospora, and to regard the para¬ 
site of the frog as its type. My own view is that it is far better to eliminate Cytospermium alto¬ 
gether, on the grounds that it was never defined, and included a heterogeneous assemblage of 
forms. 
