STUDIES ON AVIAN H^MOPROTOZOA. 711 



prove of considerable help in this connection. It is this: 

 Parasites exhibiting a trypaniform condition in a 

 blood-suckins* insect must be considei-ed as belono-- 

 ing to the life- cycle of a vertebrate trypanosome, 

 until the contrary is definitely established; and the onus 

 probandi lies with those who maintain the opposite view. 



Another conclusion which appears indicated is that, iji 

 general, such parasites do not pass into a true herpetomonad 

 condition; in other words, they have not a definite herpeto- 

 monad phase in the life-cycle. Bearing in mind that many, 

 at any rate, of the vertebrate trypanosomes which have an 

 insect as their alternate host are almost certainly to be 

 derived from a herpetomonadine form, which was originally 

 a parasite solely of the insect, it will be understood, of course, 

 that in certain circumstances the parasites may revert, as 

 it were, to a pseudo-herpetomanad condition, or even to a 

 herpetomonad one, as I have found in the case of my avian 

 trypanosomes in cultures. But with this qualification, all the 

 observations so far recorded point to the above conclusion. 



As a matter of fact, the occurrence of typical herpetomonad 

 forms in blood-sucking insects has not been described in 

 neai'ly as many cases as would appear, at first sight, to be 

 the case. In many of the papers that I have seen which 

 profess to describe such forms, a study of the figures shows 

 that the authors have been dealing really with trypanonionad 

 (crithidial) forms ; these are merely further instances of the 

 confusion formerly existing in regard to the diagnosis of 

 these two types. Thus the Herpetomonas algeriense 

 described by the Sergents (28) from Culex pipiens does 

 not appear to have anything in common with a true Herpe- 

 tomonas; from the figures given it must be regarded as a 

 trypanomonad form.^ 



' Instances, on the other hand, of what are apparently trne herpeto- 

 monad forms occurring in mosquitoes and restricted to this host ai-e 

 given by Patton (' Brit. Med. Journ.,' 1907, ii, p. 78) and also by the 

 Sergents (I.e.) ; but there is not likely to be any difficulty in distinguish- 

 ing such parasites from phases of a vertebi-ate trypanosome. I may 



