372 
Leishmania, Herpetomonas, and Crithidia 
without the flagellum (Plate XXI, figs. 37, 38); Crithidia pulicis discovered by 
Porter in Pulex irritans may even reach a length of 65/z, including the fla¬ 
gellum (Plate XXII, fig. 12); and Crithidia hystricopsyllae discovered by 
Mackinnon in Hystricopsylla talpae is 18 /jl long, without the undulating mem¬ 
brane and the flagellum (Plate XXII, fig. 8). Forms notably larger than 
Leishmania are found also in Herpetomonas ctenopsillae described by Laveran 
and Franchini. 
The anterior end of the young pear-shaped forms of Leishmania is rounded 
and is crossed by the flagellum, while in the Insectan Flagellates it is always 
pointed and drawn out along the flagellum. The posterior end of these forms 
in Leishmania is pointed and almost conical, while in the insectan flagellates 
it is rounded. Leishmania also sometimes shows the anterior end slightly 
pointed and the posterior end rounded (Plate XXI, fig. 31), but in this case 
the parasites are always short and thick, with a very short flagellum, and the 
blepharoplast is very close, or attached to the nucleus; these individuals 
represent only a stage leading on to the post-flagellate form. 
The elongated forms of Leishmania in fleas, which are absolutely identical 
with the cultural forms, show a pointed anterior end, from which the flagellum 
projects, and a posterior end, which is abruptly truncated, almost conical. 
It is to be noted, however, that in the Herpetomonas described by Mackinnon 
in Ctenophthalmus agyrtes (Plate XXII, figs. 1-4), and by Wenyon in Pulex 
irritans, the posterior end is drawn out in a filiform prolongation (Plate XXI, 
figs. 37, 38). 
Finally, Leishmania is differentiated from Crithidia by the complete ab¬ 
sence of an undulating membrane (Plate XXII, figs. 8, 12, 13, 14, 15). 
Herpetomonas and Crithidia of fleas, according to Mackinnon, Noeller and 
Fantham, may show large forms, which are rounded or elongated (Plate XXII, 
figs. 5, 6,11); in this case the ends are rounded or obtuse, the parasites possess a 
large nucleus and blepharoplast, and many granules distributed through the 
vacuolar plasma (Plate XXII, figs. 8, 11); the flagellum in these forms is very 
short and is continued into the body of the parasite as a conspicuous rhizoblast, 
more or less deeply coloured. I have never seen similar forms in the develop¬ 
mental cycle of Leishmania in fleas. 
In studying the relations between Leptomonas of Ctenocephalus canis and 
Leishmania of human and canine origin, Chatton has recently observed that 
in cultures of Leptomonas ctenocephali large forms appear which he calls 
“aciculees flagelles,” which present a body “rubanne' 1 and u torder. ,? We can 
thus distinguish at once between the cultural forms of Leptomonas cteno¬ 
cephali and those of Leishmania. 
Also the Herpetomonas discovered by Balfour in Pulex cleopatrae has cer¬ 
tain stages, the dimensions and morphological characteristics of some stages 
of Leishmania in human and canine fleas; these, however, are differentiated 
morphologically in other flagellate stages, when the posterior end is filiform, 
as in the Herpetomonas found by Mackinnon in Ctenophthalmus agyrtes and by 
