C. Dobell 
179 
(see Text-fig. 2, p. 192). It appears highly probable, therefore, that the 
hepatic coccidium of man is not Eimeria stiedae, but a smaller and similar form 
which requires further investigation. 
The two new species of Eimeria discovered in the faeces of man—that 
described by Wenyon (1915 b), and the form described in the present paper- 
are still less like E. stiedae. They cannot possibly belong to this species 1 , and 
must be regarded as new. There is, indeed, a possibility that Wenyon’s 
Eimeria is E. falciformis —the species which commonly occurs in the mouse. 
But there is no evidence to prove this, and it is, I think, preferable to regard 
the two forms as separate species. There are many good reasons for believing 
that most of the protozoal parasites of the human bowel are peculiar to man- 
not forms proper to other hosts, and accidentally acquired by him. Many facts 
point to this conclusion. 
It seems clear, then, that there must be at least four distinct species of 
coccidia, belonging to two different genera, which are able to parasitize human 
beings. These are (1) Isospora hominis , already long known, but until the 
work of Wenyon, ill described; (2) a species of Eimeria discovered by Wenyon, 
resembling the form found in the mouse, but hitherto unnamed; (3) another 
species of Eimeria , to be described and named in the present paper; and (4) 
probably a third species of Eimeria , which, unlike the three intestinal parasites 
just enumerated, inhabits the liver. This last organism has been seldom seen, 
imperfectly studied, and incompletely described; so that it is not only un¬ 
named but at present unnamable, because the characters upon which its 
specific determination depends are as yet unknown. 
These conclusions appear to me to be fully justified; and I take them 
accordingly as a basis upon which to build a systematic account, which now 
follows, of the coccidia of man. 
PART II. 
SYSTEMATIC AND DESCRIPTIVE. 
In this section I propose to give a brief systematic account of the four 
coccidia of man whose existence has been inferred from the facts analvsed in 
the foregoing pages. I shall describe each species, as far as this is possible in 
the present limited state of knowledge, of all these parasites, and add such 
further details concerning their distribution, pathogenicity, etc., as can be 
gleaned from all available sources. 
It has already been pointed out that one of the four parasites to be con¬ 
sidered is a species of the genus Jsospora , whilst the other three probably all 
belong to the genus Eimeria. It is necessary, however, to say something more 
about these two genera, as they offer certain difficulties to the systematist. 
1 Cf. figs. 2 and 3, PI. VIII, and Text-fig. 2, B. 
