370 
Leishmania, Herpetomonas, and Crithidia 
length, exclusive of the flagellum, and 2-4/z in breadth (Plate XXI, figs. 24, 
25, 26). The blepharoplast is situated in front of the nucleus, to which it is 
more or less contiguous (Plate XXI, figs. 24, 26) ; in parasites which are nearing 
the post-flagellate stage it is situated laterally to the nucleus (Plate XXI, 
fig. 25). The flagellum may attain a length of 20-22/z; it may develop from a 
basal granule (Plate XXI, figs. 25, 26, 27), or directly from the blepharoplast 
(Plate XXI, figs. 28, 29). 
The elongated parasites (Plate XXI, figs. 27, 28, 29) are also morpho¬ 
logically identical with the cultural forms; they reach a size of 9-11 g in length 
by about 2 /z in breadth; their anterior extremity is pointed; the posterior end 
is conical, as in the pear-shaped forms. Thus, as in the cultural forms, the 
various “ organellae” may have different shapes and positions in different 
flagellate individuals. 
Leishmania in the flagellate stage reproduces itself in fleas by longitudinal 
division (Plate XXI, fig. 28); this takes place in the same way as that described 
for the cultural forms. Either the flagellum, or the blepharoplast, or the 
nucleus may divide first; the plasma divides last. Two equal parasites are 
thus produced, and I have never met with unequal division. 
In my numerous researches with naturally infected fleas I have very rarely 
found this flagellate stage; it has seemed to me that this stage may have some 
connection with the nutrition of the flea; I have more easily found it in fleas 
whose mid-gut still contained some undigested blood. This observation is of 
considerable value; if it should be confirmed it will provide a distinctive 
character between the developmental forms of Leishmania in fleas and the 
common Herpetomonas and Crithidia of insects, because these latter constantly 
show all stages, both flagellate and non-flagellate. 
The flagellated Leishmania , after more or less active multiplication in the 
intestine of the flea, undergoes certain modifications in structure; the ble¬ 
pharoplast first approaches the nucleus, in some cases coming to lie beside it, 
the basal granule follows and, in this stage, the flagellum is attached along the 
anterior third of the body (Plate XXI, fig. 25). In successive stages the an¬ 
terior, rounded extremity of the parasite becomes pointed and a very short 
flagellum projects from it; the posterior end, which was pointed, almost 
conical, becomes rounded and the parasite assumes a pear-shaped form (Plate 
XXI, fig. 30) ; later, the flagellum entirely disappears (Plate XXI, figs. 31, 32), 
the plasma appears of a red colour, the nucleus, the blepharoplast and the 
basal granule of a deep red colour; still later, the basal granule disappears, 
the blepharoplast becomes absorbed in the nucleus (Plate XXI, fig. 33) ; finally, 
the nuclear chromatin breaks up into numerous granules distributed in the 
plasma (post-flagellate stage) (Plate XXI, fig. 34). These post-flagellate bodies 
become provided with a cystic membrane and then the internal contents stain 
with difficulty. Cystic forms of flagellate Protozoa have been described; e.g ., 
cysts of Trypanosoma grayi in the mid-gut of Glossina palpalis, which were 
discovered and described by Minchin. During encystment I have never ob- 
