790 E, A. MINCHIN. 
a fixative, and I have always found this mixture to give the 
worst results of any that I have tried as regards the general 
form of the body (compare my figs. 36-38). 
It does not, however, follow that because the external 
form is distorted the internal structure is necessarily falsified. 
I have got the sharpest differentiation and clearest pictures 
of the cytological details in preparations fixed with sublimate 
mixtures, in which the body as a whole is undoubtedly dimi- 
nished in size. But I do not think that the technique of 
Salvin-Moore and Brein! (1907) gives them any right to deny 
the very obvious trimorphism seen in I’. gambiense, for 
instance, since their preparations, to judge by their illustra- 
tions, are obviously inferior to the ordinary osmic-vapour 
Romanowsky preparations for a study of the form, size, 
and general structure of the body. I have elsewhere contested 
their statement that T. gam biense shows no form-differentia- 
tion. ‘'T’. lewisi, on the other hand, is certainly remarkably 
uniform in structure during the non-multiplicative period. 
It is not possible to distinguish any distinct types of form, 
nor anything but slight variations in size, aS shown in my 
table above. The differences that can be observed in the 
kinetonuclei of different forms are dealt with below. 
(2) The Periplast. 
That trypanosomes have a fairly strong and resistant mem- 
brane or cuticle at the surface of the body is obvious from 
the manner in which they preserve their body-form under 
trying circumstances: ‘This fact is brought home to anyone 
who has studied the trypanosomes and trypanoplasms of 
fishes. As I have shown elsewhere,! in smears of fish-blood 
dried before fixation the trypanosomes may be almost perfect 
in form and appearance, while the trypanoplasms side by 
side with them in the same preparations are deformed almost 
beyond recognition. This alone is a sure indication that the 
body-cuticle, commonly termed periplast, is very delicate in the 
trypanoplasms but comparatively strong in the trypanosomes. 
' «Proce. Zool. Soc.,’ 1909, pp. 3—31, Pls. I—V. 
