NEW TYEE OF I’HOTISTAN PAKASITE. 
435 
riuuen, a large proportion of the crescents are usually 
actively motile. As already mentioned, Selenomastix 
})ossesses a single, ^ relatively large flagellum, whicli appears 
to be inserted in the body, as a rule, about tlie middle of the 
concave side (Text-figs. A-E). The movements are very 
varied. We have distinguished the following kinds, but 
Text-figs. A — G. 
b,- ! ' ‘ 
- ■ , ■/ 
B CD 
F G 
Crescents drawui either living or after fixation with osmic acid 
vapour. A-C seen from the side ; D and E showing the origin 
of flagellum from concave face ; F and G two different stages 
in division. 
though we have studied them very closely we are in some 
cases not quite certain how they are caused. (1) The 
flagellum is directed behind and undoubtedly acts as a 
pulsellum, causing forward progression of the bod\q in a 
rather irregular, zig-zag, but not spiral manner. We have 
nob observed a definite reversal of the direction of this 
movement, i. e. in the opposite sense, the other end of the 
creature suddenly leading the way. This appears to be the 
^ Many of the crescents have two flagella, but these are individuals 
undergoing division (Text-figs. F and G). 
