W. S. Patton 
123 
We cannot then agree with Brumpt that the haemoflagellates of verte¬ 
brates are common intestinal parasites of invertebrates. 
We have noted above that Leger has advanced much the same 
idea, and he believes that the flagellates of vertebrates were once true 
insect forms which have gradually become adapted to the blood ingested 
by invertebrates, and have in process of time become transferred to 
vertebrates. This is a very simple and convenient hypothesis, but 
unfortunately there is at present no proof in support of it; we do not 
know of a single vertebrate trypanosome which passes its sexual cycle 
in an invertebrate, that is, its life cycle does not consist of an alternating 
blood and gut parasitism. 
Where then have the trypanosomes come from ? In studying the 
methods of development of T. lewisi and T. rotatoriwm in their 
vertebrate hosts, it is clear that they exhibit changes very similar to 
Herpetomonas and Grithidia ; according to Salvin-Moore and Breinl 
T. gambiense and T. equiperdum also exhibit such stages. These facts 
suggest that the ancestor of the present true trypanosome of the blood 
of vertebrates was a crithidia-like flagellate. The interesting question 
is, was this crithidia-like ancestor a blood parasite or an intestinal form ? 
At present it is impossible to answer this question, as no true trypano¬ 
some has been found in the intestinal tract of a vertebrate or invertebrate. 
The only instance of what may be a trypanosome has been recently 
described by Chatton and Alilaire (1908) from the malpighian tubes of 
a non-biting fly Drosophila, confusa. We do not consider this parasite 
is a true trypanosome, because the authors have not worked out its 
complete life cycle, and may quite well have mistaken a particular stage 
in its life history for a trypanosome (see p. 119). Even admitting that 
this parasite is a true trypanosome, its occurrence in the intestinal 
appendages of a non-biting fly is exceedingly difficult to explain. 
The greatest obstacle in the way of understanding this group 
of blood parasites is the fact that, although they have a common 
morphological structure, they exhibit great variation in their length, 
breadth and other minor details, and most important of all we know 
practically nothing regarding their life cycles. An important advance 
however in the study of these parasites has recently been made by 
Salvin-Moore and Breinl; these authors have brought forward observa¬ 
tions on certain trypanosomes, which suggest that they pass the most 
important part of their life histories in the blood and organs of 
their vertebrate host. Let us take T. lewisi as an example, this flagellate 
(see Nuttall, 1909) can be readily transmitted to white rats by means 
