ON THE SUBJECT OF PLAGUE 
875 
In Europe, the common rat-flea is the Ceratophyllusfasciatus , 
which occupies in point of numbers a similar position to P. 
cheopis in tropical climates. 
Now to point out the differences between those I have 
mentioned. They have all well-developed eyes, with the 
exception of Ctenopsylla musculi. Of the remainder, Cerato- 
'phyllus fasciatus and P. felts have a prothoracic comb of 
bristles and the latter also a perioral comb, which are absent 
in P. cheopis, P. irritans, and Sarcopsylla gallinacea. The 
last named can readily be distinguished from the other two 
by its angular fish-shaped head and its largely developed 
mandibles. We are left now with the two important ones, 
P. cheo'pis and P. irritans. 
The plague flea has been given various names by workers 
who thought they were dealing with new varieties. Thus 
Taraboschi in Italy called it P. murinus, Tidswell in 
Sydney P. jpallidus, and Herzog in Manila P. jphilijppinensis. 
Bothschild identified all these as P. cheojpis and P. irritans. 
These may be differentiated from each other as 
follows : — 
cc 
