120 
JIUKIEL KOBEKTSOX. 
and Flemming’s fluid. The stains used were iron liaema- 
toxylin, Delafield’s lisematoxylin, Twort’s combination of 
licht-griin and neutral red, and acid fuchsin. Tliese are all 
useful stains. The Gienisa dry film method has been so much 
criticised that one felt that cytological work carried out with 
this stain was on an insecure basis until confirmed or criti- 
cised by other methods. 
The corrections in this paper apply only to cytological 
detail, and my view of the life cycle, as a whole, has only 
received further amplification from the new facts at my 
disposal. 
In the spring of 1907 I received a number of Pontobdella 
cocoons from the Marine Station at Plymouth ; they had been 
deposited on clam shells. I put them into a glass jar filled 
with clean sea water, covered it with a loosely-fitting glass 
lid, and simply put it on to a shelf in the laboratory. I went 
to Ceylon in the course of the summer, and was later informed 
that the leeches hatched out about the beginning of October, 
1907, although the exact date was not noted. On my return 
in the autumn of 1908 they were still alive in the original jar 
and the same water. In November I took them to the 
Marine Station at IMillport,^ on the Clyde, and fed them on 
infected skate to obtain the first stages of the parasite in the 
leech. 
I may say in passing that the Trypanosome infection is 
vei’y common in the skate caught in the Clyde area; more 
than 50 per cent, of these fishes are infected, a circumstance 
which accounts for the great frequency of the parasite in the 
leech, only occasional specimens being uninfected. 
The leeches, it was observed, showed the greatest excitement 
— waving about actively in all directions — when a shadow 
was made to fall upon the jar containing them. This reaction 
to the appearance of a shadow is very marked indeed, and 
must be of service to the creature in its natural state. The 
' I wisli to expre.SK my thanks to the director of the station for 
affording me all iiossihle facilities in carrying out these experiments. 
