266 Herpetomonads 
within the cyst, or by the more elaborate processes ot autogamy with 
their attendant karyoplasmic readjustments. The figures and descrip¬ 
tions given by authors (Patton, Berliner, 1909), though not conclusive, 
suggest that any sexual process may be looked for in the cyst, and is 
possibly an autogamy. 
B. Observations on the living organism. 
The study of stained material alone is often misleading, and should 
always be supplemented, where possible, by observation of the living 
organism. I cannot help thinking that, if this method had been resorted 
to in the first instance, Herpetomonas would now have been described 
as having a double flagellum 1 . 
In the case of the fly, one is often able to keep the flagellates under 
observation in their natural medium, for the wall of the gut is sufficiently 
transparent to admit of accurate observation of its contents. In the 
larva this is usually not possible, as there is a great abundance of dark- 
coloured semi-fluid material in the gut. It is very interesting to watch 
the flagellates attach themselves to the wall of the intestine, and collect 
there in groups and clusters during the early stages of the encysting 
process. 
More often I simply teased out the gut-contents in a drop of normal 
salt solution, and sealed the coverslip well down with wax. The 
flagellates live under these conditions for as long as 36—40 hours. The 
adult flagellate moves with extreme rapidity, the body rigid and 
vibrating like a compass needle from a point about half-way down its 
length, under the ceaseless lashing of the stout flagellum 2 . Very 
conspicuous are a number of strongly refractive granules in the posterior 
end of the body. With good lighting the tropho- and kineto-nuclei 
and the rhizoplast can also be clearly seen. I have frequently watched 
the process of longitudinal division. The second flagellum can be seen 
as a short process springing up at the base of the old flagellum: it 
increases rapidly in length, and follows the movements of the old 
flagellum exactly, as though the two were enclosed within the same 
sheath, or else simply adherent to one another. In this condition they 
may remain for some time. The body of the animal now begins to 
split longitudinally, starting from the anterior end, and the two flagella 
1 Berliner (1909) and Porter (1907) have given accounts of the division of Herpetomonas 
jaculum in vivo. 
2 The movements of Herpetomonas have recently been well described by Porter (1909). 
