678 MURIEL ROBERTSON. 
about an hour, and then cease and move about on the cara- 
pace, or even leave the tortoise altogether, and upon being 
replaced would take a second meal. I was in some doubt as 
to whether the leech had always fed the first time, but in a 
few cases it certainly had, and it had generally made the 
characteristic little wound. ‘This habit, I think, may have a 
certain importance, owing to the very rapid changes which 
take place in the Trypanosome in the crop. I do not wish to 
imply that the horse-leech is likely to be a facultative trans- 
mitting host for this particular Trypanosome in nature, but 
the fact is of interest in regard to the transmission of para- 
sites by leeches generally. 
Text-Fic. 4—Poecilobdella granulosum feeding on 
Emyda vittata. (Drawn by A. K. Maxwell from a sketch 
by Dr. A. Willey.) 
The time taken to digest a meal appears to be much shorter 
in the Ceylon freshwater-leech than, for instance, in such a 
creature as Pontobdella muricata, the common marine 
leech which infests the skate of Huropean seas, where very 
many months elapse before digestion is complete. Thus one 
of the Ceylon leeches which had fed vigorously so that it had 
been seen to swell out to a great extent, was nearly empty 
as regards its crop after fifty-three days. The size of 
the leech has, of course, a good deal to do with the length of 
time taken to digest a meal, a big leech taking longer than 
asmall one. I should say that about two to six months was 
the time taken to complete the digestion of a meal. I have 
no idea how long elapses in nature between the completion 
