Flagellate stage.—A. small pink staining band appears at the periphery of the cell usually
close to the blepharoplast (Figure 2) and as growth proceeds it is seen as a pink rod attached
along the margin of the cell (Figures 3 and 4). This pink staining filament represents
t h e f l a g e l l u m a n d i t s h o u l d b e n o t e d t h a t i n s t e a d o f a t o n c e p r o j e c t i n g f r e e l y f r o m t h e p a r a s i t e , a s
in the case of Herpetomonas, it is attached to the margin of the body by a rudimentary undulating
membrane. The blepharoplast next passes towards the nucleus, it then elongates and
splits transversely into two (Figure 4) and the flagellum at the same time divides longitudinally
(Figure 4). The nucleus now enlarges and is seen to contain a large number of chromatic-
granules (Figures 4 and. 5). Later it divides and the parasite itself now splits longitudinally
into two (Figure 6). On the separation of the two parasites each in turn begins to divide again
the flagellum and blepharoplast dividing first and then the nucleus so that a rosette of parasites
is produced. The round flagellating forms on separating soon begin to elongate (Figures 7
and 8) and owing to the active movements of the flagellum and its extensive attachment to the
body of the parasite, the anterior end is drawn out to a fine point (Figure 8). On the
elongation of the posterior end a typical adult Crithidia is produced (Figure 9). In the fresh
condition these rounded flagellates can be watched undergoing this process of elongation.
While the above changes are taking place the blepharoplast, flagellum and nucleus divide so that
parasites of varying sizes are produced.
The adult flagellates vary in length from 15 μ to 45 μ and from 2 μ to 4 μ in breadth; their
posterior ends may be blunt or pointed while their anterior ends are always attenuated being
drawn out into fine points. Their nuclei are usually oval and are situated about the centre of
the body of the parasites while the blepharoplasts are from 1 to 1.5μ in front of the nuclei.
Their flagella arise from a point in close proximity to the blepharoplasts but are never directly
attached to them, and passing along the attenuated anterior ends finally projecting freely. As
division takes place at all stages in the growth of these forms, parasites of all sizes may be
produced, so no importance can be attached to the length of these flagellates (Figures 10, 11 and
12). As the result of the division of an oval flagellate two shorter forms are produced and these
in turn are capable of dividing again and producing still smaller forms (Figures 13, 14, 15 and
16). The thin spirochæte-like parasites are formed by the longitudinal division of the long thin
flagellates (Figures 17 and 18). In all these flagellates the position of the blepharoplast, the
attenuation of the anterior end and the rudimentary condition of the undulating membrane are
the important points to note, these being characteristic of the Crithidia.
The round or oval forms with or without flagella cannot be considered as gregarine forms
or resting parasites but are young growing forms. It was impossible to recognise any sexual,
dimorphism in the adult flagellates as the extreme differences in size only represent early and
late stages of longitudinal division. None of these forms were seen conjugating.
Post flagellate stage.—On smearing out and staining with Giemsa the rectums of adult bugs,
in addition to the ordinary flagellates described above, a number of parasites exhibiting the,
earliest changes towards encystment were seen (Figure 19). The central portion of the bodies
of some of the parasites were globular, the posterior ends were shortened, while the anterior ends
were drawn up (Figures 19 and 20). At the same time as these changes are taking place the
nucleus, becomes situated towards one end of the parasite while the blepharoplast is usually
situated close to it. As the anterior end of the parasite shortens the flagellum gradually
becomes more and more free so that eventually it is only attached by a short intra-cellular
portion (Figures 21, 22, 23, 24, 25, 26, 27, 28 and 29). The parasites are now oval or circular
in shape, their protoplasm stains dark blue, is granular and slightly vacuolated. The attached
portion of the flagellum next becomes absorbed as it can no longer be seen passing into the
body of the cell. It is important to note that these encysted forms vary considerably in size so
that it is most probable they originate from more than one type of the elongated flagellates.
The cysts (Figures 30 and 31) are passed out in the fœces together with numbers of flagellates
some of which have degenerated.
Although a careful search was made for the parasites in the ovaries and eggs, they- were
never seen in any other situation than the alimentary tract. It should however be borne in
mind that it is extremely difficult to demonstrate the parasites in the eggs so that the mere fact
of not finding them in this situation does not necessarily exclude the possibility of their being
transmitted hereditarily.
THE GENUS CRITHIDIA—LEGER.
In 1902 Leger created the genus Crithidia for a flagellate which he found in the alimentary-
tract of Anopheles maculi penuis naming it Crithidia fasciculata and in his description he
recognised two forms, oval and attenuated. Leger based the genus on the short oval or
truncated form of the parasite ; a reference to Leger's figures of Crithidia fasciculata however
clearly shews that the short forms are the immature stages of the parasite. The adult parasite
is exceedingly characteristic, its anterior end is elongated and drawn out, the flagellum being
attached to it by a narrow rudimentary undulating membrane. From a reference to my
description of Crithidia gerridis it will be seen that the short oval forms are the young or