126 
Loa papionis n. sp. 
to make its central spot the most prominent object in the whole larva; at 
this stage of differentiation, red streaks are to be seen between the cells and 
their respective pores. If the preparation be a little less differentiated, the 
red streaks reach from pore to pore but are absent in front of the excretory 
and behind the anal pore. If still less differentiated, the pore-chambers and 
central viscus take the red stain, and finally the pvronin predominates every¬ 
where. 
These formations are usually well shown after treatment with iron haema- 
toxylin (Plate VIII, fig. 3, Ex.C., G.C.). The central spot appears as a black, 
homogeneous body in a more lightly siderophile frame, the shape of which 
varies as previously described; no streaks are to be seen, while the cell outline 
is often feebly or not at all indicated. In dry blood-films stained by the pan¬ 
optic method or with Giemsa, these cells are invisible; whilst in films stained 
by the panoptic method immediately after drying, the protoplasm between 
the body nuclei is coloured a dark green or blue in the neighbourhood of the 
pore-chambers (Plate VIII, fig. 1), while the pore-chambers themselves may be 
lightly tinted in the same way. After “vital” staining with azur II, the pore- 
chambers are coloured first, the excretory and genital cells next, and last of 
all the subcuticular and body nuclei. 
Conclusions. Although I have followed the terminology of Rodenwalt in 
referring to the excretory and genital cells, I have only done so in order to 
facilitate their description. I am unconvinced as to their cellular structure for 
the following reasons: 
(1) These so-called cells are frequently not individualised at all. 
(2) When present, their outline may either be double or incomplete. 
(3) I was unable to demonstrate the presence of chromatin or anything 
resembling a true nucleus. 
An interpretation of these formations. The following facts would seem to 
indicate that—whatever the ultimate destiny of these formations may be 
they function temporarily as part of an excretory apparatus, the products of 
excretion being eliminated by the pores. 
(1) The presence of streaks, extending from the neighbourhood of the 
central viscus to the pore-chambers, along the course of which the so-called 
excretory and genital cells may be developed, is especially well shown on 
differentiating preparations fixed wet and stained with carbolmethylgreen- 
pyronin; moreover these formations are the last to loose the pyronin. 
(2) After vital staining with azur II, the pore-chambers, together with 
the excretory and genital areas, are coloured before the subcuticular and body 
nuclei. 
The central viscus. The central viscus is frequently stated to represent the 
remains of the vitellus and to consist of reserve material, but it does not exist 
in coiled embryos, and is small or absent during the uncoiling process; 
moreover, it is frequently small or invisible in larvae from the blood. In the 
