122 
>rUKIEL ROBEFrrSUN. 
skate till the moniing of the IGth, but did not seem to feed 
again. 
Anyone who has reviewed a large number of a given 
species of leech will have observed that there is a good deal 
of individual variation in the processes of digestion. The 
broad lines are of course the same, but there is always a 
certain amount of individual idiosyncrasy. This in Ponto- 
b del la is chiefly expressed in the greater or less fluidity of 
the blood in the crop and the nature of the bacterial flora 
moulds, schizomycetes, etc., present. These complex circum- 
stances no doubt react upon the Trypanosomes and may 
explain a certain variability in the detail and also in the time 
co-efticient of some of the developments. 
The blood in the crop of Pontobdella has a tendency to 
coagulate. It forms a rather dry mass with fluid in the 
interstices. The time factor in this stiffening of the blood is 
rather variable. It always occurs, but the time at which it 
happens and the length to which it goes differs a good deal 
in individual specimens. Late in digestion the mass in the 
crop tends to become fluid again. 
In Pontobdella the crop is a single rather thin-walled 
sac passing back from the oesophagus right to the posterior 
end of the body. The opening from the crop into the intes- 
tine is placed at a point about two thirds of the way from the 
anterior end and it passes back as a narrow tube lying on 
top of the crop. 
The young Pontobdella which had been hatched in cap- 
tivity were opened at different intervals after feeding on 
infected skate. 
The condition of the parasites was carefully observed and 
the following course of development was found to take place. 
It must be observed in ])assing that skaters blood contains an 
immense number of leucocytes, which present very con- 
fusing appearances; also the parasites are rather scarce until 
the multiplication period sets in. ksome searching is there- 
fore required to find the Trypanosomes in the earliest stages. 
