C. Dobell 
iso 
The oocysts are passed in the faeces with their contents already completely 
differentiated. In this respect, therefore, they resemble those of E. wenyoni 
and differ from those of I. hominis. In almost every other way, however, they 
are strikingly different from those of E. wenyoni —and, in fact, from those of 
every other species of Eimeria with which I am acquainted. The oocyst 
(Plate VIII, fig. 3) is spherical, with a diameter of about 36p,. Its wall is com¬ 
posed of at least two distinct layers—an inner, fairly thick and uniform, and 
an outer which appears composite, and is incrusted with adherent bacteria 
and other foreign particles from the faeces. The wall as a whole is faintly 
yellow in colour, but is quite transparent, so that the entire contents of the 
oocyst can be very clearly seen. 
The oocyst contains, in addition to the four dizoic spores characteristic of 
the genus, a small oocvstic residue composed chiefly of \~ery brightly retractile 
granules, which may be more or less dispersed. The spores themselves are long 
and sharply pointed at both ends, their shape being like that of a whetstone. 
Their length is 30/x-32/r, and their width in the middle about 7*5 /jl. The 
sporocyst is composed, as usual, of a tough and uniform inner coat (endospore) 
and a deciduous thin outer membrane (epispore). The remains of the latter 
give the external surface of the spore a slightly uneven or frilled appearance, 
noticeable chiefly towards the extremities. 
The two long and slender sporozoites lie within the spore, which they 
almost fill, in the typical manner, with their anterior ends 1 directed towards 
opposite poles. The anterior end of each is pointed, and wrapped round the 
posterior end of its fellow. The posterior end is rounded, and contains an oval 
body, lying subterminallv, which is probably the nucleus. Between the latter 
and the posterior extremity there are always present two or three very bright 
and small bodies 2 , fusiform in outline and longitudinally disposed. (Cf. fig. 3, 
PL VIII.) A few small and rather feebly refractile granules lie anterior to the 
nucleus and extending for a short distance forwards along the body of the 
sporozoite. There is a relatively small sporocystie residue, represented by a 
few bright and scattered granules lying near the middle of the spore. 
The foregoing account is based upon a careful study of the living oocyst, 
as I have not been able to obtain any stained preparations. All the structures 
described are, however, easily made out in the living organisms; and they are 
shown, as accurately as possible, in fig. 3, PL VIII. Dr A. C. Stevenson, of the 
Wellcome Bureau, kindly photographed the oocyst from which this drawing 
was made. Unfortunately, however, the object is a very unsuitable one to 
photograph, as the spores all lie in different planes, and consequently cannot 
all be shown clearly at the same time. The photograph, though forming a 
1 I use these terms—anterior and posterior—for the ends which appear to correspond to the 
fore and hind extremities of other coccidial sporozoites which I have been able to study in greater 
detail—especially those of Aggregate and Adelea. 
2 I do not remember to have observed similar structures in the sporozoites of any other 
coccidium. 1 do not know what they are. They have a very bright and almost crystalline appear¬ 
ance. 
