5
. •considerable length. Their anterior ends are rounded and never pointed. They have
t h r e e e c h h a r a c t e r i s t i c s t a g e s i n t h e i r l i f e c y c l e s : — ( 1 ) P r e f l a g e l l a t e , r o u n d , o r a l o r p e a r - s h a p p e d b o d i e s w h i c h m u l t i p l y b y
simple longitudinal division or by multiple segmentation (2) Flagellate stage, when they multiply by
longitudinal division which may be equal or unequal; in . this stage they often exhibit marked polymor-
phism-(3) Post-flagellate stage, when the flagellates collect in the hind guts of their hosts where they
shorten, D ivide, sometimes more than once and finally encyst. These cysts are passed cut in the foes
of the ham and are reingested by fresh hosts when feeding. So far hereditary infection is not proved
to occur among this group of flagellates..
I have shown that Prowazek's interpretation of the flagellar apparatus of Herpetomonas
musc domesticwω is incorrect, and. I therefore do not see any reason for introducing the generic
name Leptomonas, as has recently been done by Rouband. From the above definition it will be
seen that the flagellate of Lygωus militaris is a typical Herpetomonas and I therefore propose
• .naming it lygωi. For a detailed comparison of this parasite with Herpetomonas donovani the
reader is referred. to my original paper.
•
C. R1 T HI DI A GE RRI DI S ( P AT T ON) .
As a result of the researches of the late Dr. Schaudinn (1904) on the evolution of Trypano-
•soma noctu ω in Culex pipiens the attention of Protozoologists has been focussed on the 'flagellates
which lead a parasitic life in the alimentary tracts of bloodsucking and non-bloodsucking
arthropods. In spite of the fact that it is now known that these flagellates are true parasites
•of invertebrates, authors are still describing them as developmental stages of vertebrate
trypanosomes. The study of these natural parasites of blood-sucking arthropods therefore has
an important bearing in elucidating the transmission of pathogenic trypanosomes one example of
which here will suffice. It has long been known that tse-tse flies (particularly G. morsitaws) are
the natural transmitters of Trypanosoma brucei and Bruce (1895-97), in his well-known experiments,
'clearly established the fact that G. morsitaws can only transmit the parasite of Nagana up to 48
hours after feeding on an infected animal. He therefore rightly concluded that the fly acted
as a simple carrier of the trypanosome. These observations have been fully confirmed in the
cease of other trypanosomes and tse-tse flies. It is also known that pathogenic trypanosomes
when ingested by tse-tSe flies do not infect susceptible animals if artificially injected into them,
unless they are removed almost immediately from the stomach of the flies. Koch, Gray,
Stuhlmann, Minchin, Keysselitz, Mayer and others have recently endeavoured to work out the
life cycles of these pathogenic trypanosomes of Africa in the Glossinω. In numerous instances
these authors fed tse-tse flies on infected animals and, on subsequently dissecting the flies, found
a large number of flagellates in their alimentary tracts. These parasites were then described as
developmental stages of the trypanosomes ingested by the flies. No proof was given as to how
the well known vertebrate trypanosomes pass into these developmental forms and no control
experiments were carried out to rigidly exclude natural flagellates of the flies. As a result of
these erroneous observations some of the authors bring forward wild hypothesis to explain the
possible life cycles of these pathogenic trypanosomes and their phylogenetic speculations can
only lead to endless confusion.
It is therefore important first to study the life cycles of these natural flagellates of blood-
sucking and non-blood sucking arthropods and above all to ascertain how they pass from one
host to another. With this information at hand it will then be possible to say whether any
particular vertebrate trypanosome undergoes a developmental cycle in an invertebrate.
The flagellate which forms the subject of this paper was therefore studied in order to work
out in detail its life - cycle and at the same tune to discover the method. by which the bugs
become infected. The parasite was first found in the alimentary tract of Gerris fossarum and
later in species of microvelia and Perittopus. As microvelia was readily obtained in large
numbers and as all the specimens examined were infected., it was selected for the study of the
parasite. For the description of the bug and the methods employed in the study of the para-
site the reader is referred to the original paper (1908) The life-cycle of the parasite may be
'conveniently divided into three stages— Preflagellate, flagellate and. Post-flagellate.
Pre flagellate stage.—In this stage, which is found in the crop of the adults and nymphs,
the parasite is a round, oval or pear-shaped body (Figure 1, la) measuring from 4 to 6 μ in
length and from 3 μ to 4 μ , in breadth. Its protoplasm is granular staining a light pink towards
the centre and deep blue all along the margin. The nucleus is a circular body which stains
light pink with Giemsa's stain and contains a number of rod-shaped. chromatic bodies which may
or may not be chromosomes.* The blepharoplast is a large 'rod-shaped structure usually situated.
towards the periphery of the cells. These parasites without dividing increase in size and may
•even measure as much as 7 μ in length. They now pass into flagellation.
According to those who believe that the methods employed, fixation by alcohol and subsequent staining by
Giemsa, give misleading results ; they are ante-facts. This is however going a little too far. In the fresh condition.
'the nuclei of some of these insectal flagellates can be seen to have a granular appearance.