260 Herpetomonads 
1. Pre-jiagellate. This stage was found occasionally in small 
groups and clusters in the mid-gut of the fly, and more rarely in the 
upper end of the mid-gut of the larva. Its comparative infrequency 
suggests that flagellation is a rapid process. I tried to induce freshly 
hatched-out flies to feed on infected food-material, in the hope of 
studying more closely the details of flagellation, but this attempt was 
unsuccessful. Pre-flagellate stages in Giemsa stained preparations are 
small round or oval bodies —Sg x 2'5 g to 4p. x Sg (figs. 1—8)—the 
cytoplasm staining intensely blue, the circular nucleus a uniform deep 
red : the kineto-nucleus 1 is a small deeply-staining rod-shaped body, 
either immediately anterior to the nucleus or slightly to one side of it: 
numerous smaller chromatin-like granules are scattered through the 
cytoplasm. The future position of the flagellum is usually already 
indicated by a rose-pink area extending from the kineto-nucleus to one 
end of the cell. Occasionally the flagellar root can already be seen 
forming within this flagellar vacuole as a darker-staining strand. The 
whole cell is in some cases surrounded by a definite cyst membrane, 
staining deep pink, but more often this has already dissolved. The 
flagellum comes to the exterior as a delicate pink “brush,” which rapidly 
takes on the more definite appearance of a stout flagellum, and proceeds 
to elongate. Division may take place even at this early stage (see 
fig. 8). 
2. Flagellate. This was by far the most common stage in the 
larva, where flagellates were found in enormous numbers in the mid-gut; 
in the adult fly they were not so abundant, but when present, were 
always in the mid-gut. 
The adult flagellates in the larva differ somewhat from those in the 
fly (cf. figs. 11 and 26). The flagellate in the fly (fig. 11) differs in no 
essential from H. muscae-domesticae, the appearance of which, in Giemsa 
preparations, is well-known. The average dimensions of a full-grown 
flagellate are 2bg x 2'hg (not reckoning the flagellum). The body is 
roughly cigar-shaped, slightly blunt behind, and furnished anteriorly 
with a long (30/r), relatively thick flagellum. The flagellum arises from 
the neighbourhood of the kineto-nucleus, but its actual origin seems to 
be in a minute granule in front of that body: to this granule the term 
“ blepharoplast ” might be more consistently applied. The root of the 
flagellum within the body of the organism is about \g long and it is 
1 I propose to follow the nomenclature of Minchin (1908) which has since been adopted 
by others. The term “ blepharoplast,” if used at all, ought in this case to be reserved for 
the granule at the base of the flagellum. 
