A. Porter 
383 
Herpetomonas for a parasite found in the alimentary tract of the common 
house-fly, the parasite having been previously described by Burnett 
(1851) as a Bodo. At that time, the genus Herpetomonas was little 
known, and the existence even of a nucleus in the parasite was doubt¬ 
ful, but one flagellum was regarded as a constant feature. Since Kent 
established the genus, comparatively many parasites have been placed 
therein, but the life-cycle of most of them is incompletely known, the 
flagellate stage of existence usually being the only one described, and 
that often imperfectly, owing to too much reliance having been placed 
on stained specimens to the exclusion of valuable facts that could be 
obtained by the study of the living organism. When the development 
and life-cycle are completely followed in the living organisms, mis¬ 
interpretation of morphological details is rendered far less possible. 
Leger (1903-4) worked on various parasites which he placed in the 
genus Herpetomonas, considering them uni-flagellate. One of these was 
H. jaculum from Nepa cinerea, the flagellate stages of which were 
described with characteristic painstaking detail. These flagellated forms 
were termed by him “ les formes monadiennes.” A second form of the 
parasite, “la forme gregarinienne” is also described as being derived 
from the first form. As these occurred in old Nepa, in the lower 
portions of the gut, they would now be considered as forms in which 
the transition to the post-flagellate stage had begun. 
Prowazek (1904) gave a long and involved account of Herpetomonas 
muscae domesticae. He described the flagellate stage of the parasite 
only, and his observations commenced on the parasite in this condition. 
Hence owing to lack of knowledge of the development of the parasite, 
there were many chances of errors of interpretation, some of which 
errors actually occurred. This account of Prowazek’s has caused 
much argument and has resulted in great confusion regarding the 
systematic position of organisms formerly considered Herpetomonads, 
but which must be assigned to other genera should Prowazek’s work be 
accepted. Prowazek declares that H. muscae domesticae has two 
flagella, these being united by means of a narrow membrane. He also 
describes copulation between sexual forms, this being preceded by a 
most complicated series of reducing divisions of both nucleus and 
blepharoplast, and also reduction of the flagellar apparatus. The 
copulation results in a cyst which is voided with the faeces. 
The subject of this double flagellum will be referred to later 
(p. 384). 
Patton (vn. 1907) in his account of Herpetomonas calicis points out 
the resemblances existing between stages of this parasite and those of 
