134 
Haemoflagellates, etc. 
already recorded are scattered in many journals, a few of which we have 
not been able to consult: further, in many instances the conclusions of 
one observer are totally different to those of another, although presumably 
both were studying the same parasite. The observations on the flagel¬ 
lates of insects recorded by most observers are so incomplete and discon¬ 
nected that, although we have made a special study of the life cycles of 
several species of Herpetomonas and Critlridia, it has been quite im¬ 
possible to place all the observations in any systematic order and to 
harmonise them with our results. We (1908) have elsewhere suggested 
that these simple parasites have a definite life history which may con¬ 
veniently be divided into three stages, pre-flagellate, flagellate and post- 
flagellate. We believe, that if they are studied along these lines, the many 
forms, which at present it is impossible to understand, will eventually be 
found to fit into their right places in the life cycles of the parasites. 
One example here will suffice. We have already noted that Chatton 
and Alilaire (1908) have recently described two flagellates from Droso¬ 
phila confusa ; one of these is obviously a typical Herpetomonas, and the 
other, which was chiefly found in the malpighian tubes of the fly, we 
believe is a Crithidia. Chatton and Alilaire however consider it is a 
trypanosome somewhat like T. dimorphon, Dutton and Todd. On 
referring to the authors’ figures of this flagellate we find it has all the 
characteristics of an insectan Gritliidia such as we (1909) have recently 
defined ; its large blepharoplast should be particularly noted. In fig. 8 
we note the flagellum does not appear to pass right up to the blepharo¬ 
plast, which is almost at the posterior end. This figure should be com¬ 
pared with our drawings of the post-flagellate stage of C. ctenophthalmi 
where a very similar appearance will be seen in the case of the flea 
crithidia. We believe then that the two flagellates of Drosophila confusa 
are quite distinct, and that one is Herpetomonas, while the other is a 
Crithidia. It is well known that both Herpetomonas and Crithidia may 
be found in the same insect. From a study of some of the figures of 
C. drosophila we believe Chatton and Alilaire are dealing with the post- 
flagellate stage of the parasite. Figs. 4, 5 and 6 depict a typical Crithidia 
in which the blepharoplast tends rather to lie behind the nucleus (see our 
figure of C. liaemaphysalidis). In studying these parasites of insects it 
is of the utmost importance to first ascertain how they are transmitted 
from one insect to another; having found this out the complete life 
cycle will in most cases be readily understood. 
