.i 5 'i 
A GREGARINE PARASITIC IN THE 
DOG-FLEA, CJENOCEPHALUS 
SERRylTICEPS 
BY 
E. H. ROSS, M.R.C.S. England, L.R.C.P. London, 
HEALTH OFFICBR. >rlZ CANAI., Fr.VPTtAN PPIU-IC HEALTH DKl’ARTMENI 
(Received for publication 29 March, 1909; 
The excuse for describing this parasite which inhabits the 
alimentary tract of the dog-flea must be in the fact that much work is 
now being done with fleas generally, and some confusion may be saved 
to others, working at these insects, if some details of its various phases 
are related. 
This parasite was found, in varying numbers, in the fleas of two 
fox-terrier dogs, mother and son, which had lived in Port Said nearly 
all their lives. Its stages follow the well-known gregarine type 
frequently found in Nematodes and Culicids. It is a Cephalin showing 
a well-marked cycle of sporogony, all the stages of which are 
completed within the body of the flea, its host ; while, like many 
other gregarines, the cycle of schizogony, so far as can be found out, 
is wanting. 
It is convenient, for the sake of description, to begin with that 
phase of the cycle which is first seen in the flea. 
I. THE EARLY TROPHOZOITE 
This stage, as in similar Gregarinidae found in the Worms, 
Echinoderms, and Ascidians, is the first resting phase of the parasite 
‘nthe flea. It is probably caused by the direct infection of a stomach 
by a sporozoite derived from the rupture of the sporocyst, the 
'■Porozoite having been eaten by the flea larva when crawling on the 
'log’s back. But It is possible that it may be derived from the 
‘'ierozoite of a cycle of schizogony which has taken place either 
’’ulside the host or within the stomach of the flea-larva ; up to the 
Present time, however, no traces of such cycle have been noted. 
