336 
A Critical Review, etc. 
mistook them for developmental forms of T. lewisi. We cannot say 
whether this parasite is a Crithidia or a Herpetomonas. Lastly, one of 
us, as mentioned above, found a Crithidia in the gut of the larva of 
Ctenocephalus felis iu Madras. The larvae of this flea suck the blood of 
the cat and wherever a tame cat used to sit larvae gorged with blood 
were found in large numbers. 
Concluding Remarks. 
It is again necessary to make some remarks on the genus Crithidia 
of Leger as we find authors are still calling certain flagellates Crithidia 
which are clearly Herpetomonads and vice versa. This genus was 
created by Leger in 1902 for a flagellate he found in Anopheles maculi- 
pennis, and the name was based on wbat Leger considered to be the 
characteristic shape of this parasite, a short truncated (barley corn) 
organism. One of us has shown that the genus Herpetomonas also has 
a very similar stage and that the short truncated forms of Crithidia 
fasciculata are its young stages. We have also pointed out that by 
following Leger’s description authors have placed a true Herpetomonas 
in the genus Crithidia, and vice versa. It is only necessary to refer to 
Leger’s (1902) original description and figures of Crithidia fasciculata, 
when it will be seen that the adult flagellate of this parasite is 
exceedingly characteristic, and we have never seen any Herpetomonas 
like it. Owing to the fact that observers have so far only studied 
stages of these parasites, it can readily be understood how errors have 
arisen. 
A great deal of the confusion regarding these flagellates is also 
undoubtedly due to Prowazek’s erroneous view of the flagellar apparatus 
of H. muscae domesticae. One of us has shown clearly that, apart from 
the study of the flagellate stage of Herpetomonas muscae domesticae, by 
following the pre-flagellate stage up to the formation of the flagellum it 
can be demonstrated beyond any doubt that it has a single flagellum. 
Where then can the double flagellum come from ? One of us has studied 
this flagellate for the last two years, and will shortly give a complete 
account of it where it will be shown that a fly may be found with 
almost all the flagellates showing the appearance of the double flagellum, 
and again in another fly the majority have a single flagellum. Finally, 
in following the post-flagellate stage of H. muscae domesticae the parasites 
have been observed to have only a single flagellum. The subject is still 
more confused by the recent introduction by Chatton, Alilaire (1908) 
