C. H. Treadgold 
123 
blood-films stained by the panoptic method, it appears as a reddish granular 
mass, but after wet fixation the granular appearance is less in evidence; in 
smears treated with iron haematoxylin it appears as a siderophile body, 
while it stains red with carbolmethylgreenpyronin. The number of nuclei is 
considerably reduced in the region of the central viscus and first genital cell 
(Plate VIII, fig. 4); in stained preparations the resulting light area varies from 
50 to 60 ju in length. 
Morphology of the ova and larvae taken from the female genital tract. The 
ripe ovum measures about 25 by 18/x. The egg membrane is secreted immedi¬ 
ately after the entrance of the spermatozoon (Plate VIII, fig. 7, E.M.). At the 
stage of commencing differentiation the egg measures 41 by 28/z, intermediate 
measurements corresponding to the morula stage. The egg grows in size up 
to 55 by 37 g when the embryo commences to uncoil; the terminal flexure of 
the tail represents the last stage of the uncoiling process, and larvae showing 
this peculiarity are sometimes present in the blood-stream. Uncoiled embryos 
are possibly a little narrower than larvae from the blood, but their length varies 
between the same extremes. The egg membrane persists for a time as the 
embryonal sheath, but a variable proportion of sheathless larvae are present 
in the vagina and lower ends of the uterine tubes. I never succeeded in 
demonstrating the central viscus in young embryos, while it was small or 
absent during the uncoiling process; at this stage the anal pore chamber is 
not always visible, while the subsidiary genital cells are not to be seen; the 
nerve ring is present, but small. Little can be made out in the coiled up stage; 
but the excretory pore chamber is sometimes visible. Apart from such differ¬ 
ences, all of which result from examination at an earlier stage of development, 
the structure of the embryos from the genital tract was identical with that of 
the larvae found in the blood. 
The chief differences between Microloa papionis and Microloa loa are 
summarized in Table I. 
A Consideration of several Imperfectly Solved 
Morphological Problems. 
The sheath. In preparations made from the lower end of the genital tract 
of adult females the sheath was usually, but by no means invariably present, 
while it was seldom seen in blood-films. At first sight this seems rather re¬ 
markable, for the sheath appears to have been regarded by all observers as 
invariably present in blood-films containing Ml. loa. Is it possible that the 
presence of a sheath in Ml. loa is not such a constant morphological feature 
as it is alleged to be? The following facts would seem to be of interest in this 
connection: 
% 
(1) According to Stephens (1916), the uteri of L. loa contain eggs in the 
most various stages of development, besides hatched-out larvae. 
