A. Porter 
157 
having been described as and named Grithidicie must be considered as 
such until it can be shown experimentally that they are otherwise. 
So much for Dr Woodcock’s “ onus probandi.” 
While careful study seems to indicate that the simplest form of the 
Trypanosomatidae is Ileriietojiionas, then increase of complexity leads 
to Crithidia and still further evolution to Trypanosoma, yet this is only 
a probable line of evolution, suggestive it is true, but not proven. 
Analogy is often misleading. Amphibia such as frogs and newts pass 
through a fish stage when they are tadpoles; but fishes on that account 
are not to be regarded as merely stages in the life cycle of Amphibia : 
the same holds true of Grithidia and Trypanosoma. The value of 
analogy in dealing with the development of Trypanosomes has been ably 
summarised by Sir David Bruce and his co-workers in their recent paper 
(May, 1911) dealing with the cycle of T. gatnbiense in the tse-tse fly, 
Glossina palpalis (page 517). These workers find that T. gamhiense in 
G. palpalis practically always retains the trypanosome facies, and that 
“ Crithidia-like forms are exceedingly rare.” Further, they state that 
“because one kind of development takes place with one species of 
trypanosome and one species of tse-tse fly, it by no means follows that 
the same thing will occur either with another species of trypanosome or 
another species of fly. Each combination must be worked out separately 
and nothing left to analogy.” 
Dr Woodcock has stated that I have not attempted to prove that 
any of these Grithidia in blood-sucking Insects are true independent 
forms. I beg to differ. The statement is inaccurate and merely 
reveals the loose way in which current literature is read. In my paper- 
on G. melophagia, I regard the parasite as independent, that is, it has 
nothing to do with a vertebrate Trypanosome, for it encysts, and other 
keds by ingesting the cysts become infected. This has been shown 
experimentally on keds removed from the sheep. Further, the action 
of vertebrate blood, whether it be that of the sheep or of man, merely 
stimulates the Grithidia to divide (a most important observation which 
I commend to Dr Woodcock’s notice), no “ trypaniform ” stages were 
ever found in the keds, though hundreds were dissected during a pro¬ 
longed period. The life cycle of G. melophagia is complete in itself, with 
pre-flagellate, flagellate and post-flagellate stages (terms which I notice 
Dr Woodcock never uses—apparently preferring such fantastic and 
unnecessary ones as “ trypanomonad* ”) and there is a true hereditary 
1 Apparently this term is ^tended to have the same significance as “ crithidial,” 
a well-established term. Why, then, should Woodcock coin another term? 
