FUETHEE NOTES ON A TEYPANOSOME. 
121 
skate, coming over the ground upon whicli a leech is attached, 
will, of course, cast a shadow, and this will be one of the 
ways the leech becomes aware of the presence of its host. 
The young leeches attached themselves readily enough to 
the skate, except in one or two cases where they required a 
good deal of coaxing; ultimately, however, they all fed. 
The Pontobdella appai'ently does not feed at once, possibly 
on account of the difficulty in piercing the skin. The attitude 
of the leech when attaching itself with the intention of 
feeding is very characteristic. It takes firm hold with its 
posterior sucker, and then bends its anterior sucker in so 
that it is touching its own body. It then slides the anterior 
sucker down along the body, finally attaching it to the skate 
at a spot close beside the posterior sucker. These leeches 
made quite a large wound for such small creatures. 
In some cases, after feeding for a time, the leech detaches 
the anterior sucker, but does not, as a rule, remove the pos- 
terior one. Finally, after a greater or less interval of time 
has elapsed, the feeding is resumed. On one occasion I was 
able to observe the pimcess very clearly. A leech was put on 
to a skate at 2.30 p.m., on the 14th November, 1908; at 
10 a.m. on November 15th it was attached by the posterior 
sucker only. 'I'he leech had fed, but had not taken very 
much (the leech is, of course, rather transparent when young, 
and it is possible to tell at a glance if it lias fed or not). 
Three quarters of an hour later it was still in the same posi- 
tion, with the anterior sucker free. I then held the skate 
under water in the tank in such an attitude that 1 could see 
the leech, which had begun to make searching movements 
with the anterior sucker. It presently slid the anterior 
sucker down its body and on to the skate, but moved it 
about until it passed over the old wound, when it buried its 
sucker in it. Tlie leech seems to force its proboscis in pretty 
deep, judging from the wound and its attitude while sucking. 
At 7 ]).m. on the 15th the leech was again only attached by 
its posterior sucker, but it was much swollen, and had blood 
right up to the anterior end. It was left attached to the 
