THH STRUCTURE OF TRYPANOSOMA LEWISI. 791 
In Trypanosoma lewisi it is not difficult to discover the 
existence of a fairly thick periplast, which can be stained and 
shown up by a variety of methods. After the Romanowsky 
stain it is usually seen at the edge of the body as a red line, 
most distinct as a rule on the side opposite to the flagellum, 
where sometimes it is almost as deeply stained as the flagellum 
itself (figs. 80, 81). With Twort’s stain the periplast stains 
green and is often very distinct (Pl. 25). With iron-hemato- 
xylin the periplast stains very faintly and appears excessively 
delicate. 
In many preparations the periplast becomes very distinct, 
not by being coloured itself, but by the layer of the body 
immediately under it becoming clear and transparent, so that 
the periplast appears, on the side opposite to the flagellum, 
to stand out from the body as a delicate line, very easily over- 
looked in preparations in which itis not stained. Figs. 64-69 
show very well the genesis of this periplast-line in the process 
of extraction of Giemsa’s stain. It is also seen well in the pre- 
parations fixed with Schaudinn’s fluid followed by Twort’s stain 
(fig. 85), which colours the periplast green, as already stated. 
In preparations stained with Romanowsky stain, after being 
preserved in various ways, and either dried off or mounted in 
Canada-balsam without ever being dried, some trypanosomes 
may be found showing creases and folds of the periplast, 
which are stained red and simulate fibrils running more or 
less longitudinally (see especially figs. 70-72). I shall return 
to this point again later on. 
In or immediately under the periplast there are found in 
many species of trypanosomes, as is well known, distinct 
contractile fibrils or myonemes. I have myself seen very 
clearly, and described elsewhere, myonemes in Trypano- 
soma perce; less distinctly in Trypanosoma granu- 
losum. I found them most clearly shown in preparations 
fixed first with osmic vapour, then with Schaudinn’s fluid, 
and stained with iron-hematoxylin, very slightly extracted. 
In T. lewisi I have not succeeded in seeing myonemes, in 
spite of much searching of preparations fixed and stained in 
