G. Strickland 
229 
2 fi. The latter are very abundant indeed in the rectum. It appears 
that the large oval forms become rounded up, and that they then 
contract from side to side. 
The cytoplasm is differentiated into ectoplasm and endoplasm : in 
forms probably representing a later stage of development, the differ¬ 
entiation is extreme, a very dense-staining periplast being formed. 
The appearance thus presented is the same as that of the forms 
occurring in the ‘ crop,’ which have been described above as cysts. 
The nucleus, blepharoplast, and flagellar apparatus have even less 
chromatin than in the large oval forms. The nucleus, blepharoplast 
and intracellular part of the flagellar apparatus may even lose all their 
chromatin; the nucleus then staining pale-pink, the blepharoplast 
rosy-red, and the intracellular flagellum being invisible, probably 
because the dense periplast obscures such a delicate structure. 
The blepharoplast is now situated to one side of, or even just 
behind, the nucleus which is slightly eccentric. The rhizoplast as long 
as it contains chromatin is seen to follow the blepharoplast as this 
passes backward, although there is no visible connection between them. 
The extracellular part of the flagellum is faintly stained but is seen 
often when the intracellular part is invisible. The chromidia are very 
large in those cells in which the organella have lost most chromatin ; 
they are often with difficulty distinguished when the periplast is 
densely stained. A single chromidium away from the others is some¬ 
times seen close to the blepharoplast. The others are grouped at the 
posterior end of the cell in the periplast. (PL VIII, figs. 10-22.) 
(iii) The cysts are found in the lower end of the rectum in very 
great numbers, but are always discrete. They have been described 
above under the ‘ crop’-forms. (PI. VIII, figs. 23-25.) 
Taxonomy. 
The parasite above described must be classed with those described 
by Prowazek, Patton, Mackinnon, and others, and named Herpetomonas. 
It has been recently suggested by Miss Mackinnon (1910) that 
there has been needless subdivision of this genus into species without 
consideration of the adaptability of perhaps one species to various hosts. 
I had this in mind at the time (1909) of conducting the observations 
on this parasite, and accordingly dissected some Musca domestica, and 
Calliphora coerulea, from the same source, two butcher’s shops, as the 
Lucilia, but was unable to find herpetomonads in them. 
