W. S. Patton and C. Strickland 
337 
and Roubaud (1908) of the generic name Leptomonas of Kent. These 
observers would place all the Herpetomonad- like flagellates with one 
flagellum in this genus, while those with a double flagellum are relegated 
to the genus Herpetomonas. and Roubaud states he has observed the 
structure of H. muscae domesticae as described by Prowazek ; so have we, 
but we are unable to give any other interpretation than that given 
above: we do not know on what Roubaud’s statement is based. In 
order to make our first point clear as to how observers may be led astray 
by studying only one stage of a flagellate we will refer to another recent 
paper. Werner (1908) has described what he considers to be a Crithidia 
from the faeces of Musca domestica ; unfortunately his photographs are 
so indistinct that it is not possible to make out clearly the structure of 
the parasite. If this parasite is a true Crithidia it is obvious that the 
author has again gone back to Ldger’s definition of the genus, and we 
consider this is a serious step backwards, and that instead of helping to 
a natural classification it will lead to greater confusion. We note that 
Werner’s parasite was only found in the faeces; no mention is made as to 
whether the rectum and hindguts of the flies were examined for flagel¬ 
lates, and it is not stated whether the flies were infected with H. muscae 
domesticae as well. Werner refers to the similarity between his parasite 
and one recently described from Cidex pipiens ( H. culicis) by one of us. 
On referring to the figures of this Herpetomonas we find the only forms 
which appear to have a slight resemblance to Werner’s parasite are 
those depicted in figs. 9,10 a, 10 6. For the sake of clearness the various 
stages of this Herpetomonas were figured in a circle so that each stage 
could be readily followed. The figures to which Werner apparently refers 
clearly represent the young flagellates; it is our whole contention that 
a genus cannot be based on these immature forms. The adult flagellate 
of H. culicis is clearly depicted, and we fail to see what resemblance there 
is between it and Werner’s parasite. One of us has seen parasites very 
like those described by Werner, and we know they represent the post- 
flagellate stages of H. muscae domesticae. In numerous living specimens 
we have seen the flagellates of the house fly collecting in masses in the 
rectum of the insect where the typical long forms shorten, divide and 
eventually round up, so that we would like to know what the adult 
flagellate of Werner’s parasite is like. Remarking on the marked 
difference in size between his parasite and the flagellates of H. muscae 
domesticae , Werner believes it improbable that they could be in any way 
connected. We would draw attention to the still more marked difference 
in size between the cysts of H. muscae domesticae and the adult flagellate, 
