125 
C. H. Treadgold 
by the rapid movements of the larva in a sheath of low visibility. The re- 
fringent granule, together with the clear area behind it, would appear to be 
morphological entities, but at the present time it seems more reasonable to 
interpret these appearances as indicating the commencing formation of the 
buccal orifice and anterior part of the digestive tube, than to postulate the 
existence of a kind of sac from which an apparently useless filament is capable 
of being protruded. 
The excretory and genital cells. According to the hypotheses of Roden wait 
and Fiilleborn, the excretory cell gives rise to the excretory apparatus of the 
adult, while the first genital cell is the embryonic representative of the future 
genital system. Looss suggests that the accessory genital cells may give rise 
to the rectal ligaments and their adnexa. They and other workers assume the 
cellular structure of these formations to have been completely demonstrated, 
so before attempting to criticise the reasonableness of their belief, I will 
first of all describe these so-called cells as they exist in Ml. papionis. 
Description of the excretory and genital cells. In wet preparations stained 
with Giemsa s solution and differentiated with alcohol, these formations are 
present in a considerable proportion of larvae. The excretory cell (Plate VIII, 
fig. 2, Ex.C.) is blue in colour, more or less oval in shape, and contains a 
darkly staining homogeneous central portion surrounded by a lighter area— 
the nucleus and nucleolus of Fiilleborn. The blue outline is often deficient 
anteriorly, its lateral portions being continued forwards as two blue streaks 
which end at the periphery of the pore-chamber; when complete, this outline 
is usually continued in a forward direction as a single streak. Sometimes the 
cell appears to be double; frequently it is not individualised at all, its place 
being taken by one or more dark-blue streaks. Whether the cell is visible or 
not, these streaks are often continued in a posterior direction as far back as the 
beginning of the central viscus (Plate VIII, fig. 2, str.). 
The first genital cell (Plate VIII, fig. 2, G.C.) is larger and as a rule more 
distinct than the excretory, measuring from 10 to 15 p in length and up to 
op, m bieadth, but its shape is more variable, the ends appearing either 
rounded or square-cut. Often the outline of the cell is deficient posteriorly, 
in which case its lateral boundaries may be continued for some distance in 
the direction of the anal pore as an irregular double streak; when present, 
this outline is frequently brought into connection with the anal pore-chamber 
by an irregular series of blue streaks. Along these streaks the subsidiary 
genital cells (Plate \ III, fig. 2, S.G.C.) may be seen, but their individualisation 
is exceptional; they never exceed three in number, are quite small with a 
rounded outline, and contain a central darkly staining spot (Plate VIII. fig. 2. 
S.G.C. ). In wet preparations stained for half an hour with carbolmethylgreen- 
pyronin and differentiated with alcohol (Plate VIII, fig. 4), the subcuticular 
and body nuclei are stained green while the excretory and genital cells are 
outlined in red, the central spots are stained an intense red bv the pyromn 
and this colouration is often so marked in the case of the first genital cell as 
