PUETHEE NOTES ON A TEYPANOSOME. 
129 
unless the observation is continuous, as the infections are 
generally rather slight, and, once the Trypanosome has come 
to rest, it is not quite a simple matter to see it among the 
large number of leucocytes and red corpuscles. Moreover, 
the curious fact that all the Trypanosomes on a slide do not 
round off leads one to imagine that no development has 
taken place. 
A low temperature seems to favour the process. This 
work on the live skate’s blood Avas carried out at the Millport 
Marine Station, and the most successful set of observations 
Avas obtained in very cold Aveather, Avhen the temperature of 
the laboratory Avas much loAver than usual. 
It appears to me that these experiments Avith the young 
leeches, which confirm Brumpt’s short sketch of the life cycle 
of T. raiae, are good evidence that the Trypanosome in 
I’ontobdella is T. raiae. Of course it may be urged by 
those who do not consider that Trypanosomes have a cycle of 
evolution, however simple, outside the vertebrate host, that 
the young leeches Avere hereditarily infected Avith a flagellate 
of their oAvn. Against this I can only advance that the long 
fast of more than a year, to Avhich these neAvly hatched leeches 
Avere subjected, is not in favour of the survi\'al of such para- 
sites; and that the close correspondence betAveen the early 
stages in the leech, and those obtained upon the sealed slide 
from the skate, is strongly in favour of the identity of the 
parasites. Further, even if, in addition to the direct infection 
from the skate, a hereditary infection also exists in Ponto- 
bdella, it has still to be proved that the form inherited is 
not T. raim. 
The only Avay in Avhich quite conclusive proof of the ques- 
tion could be obtained is by means of experiments Avith both 
leeches and skate hatched in captivity. I hope ultimately to 
be able to carry these out, but the difficulties iu the Avay are 
obvious, as the obtaining of Pontob della cocoons is a matter 
of chance, and the breeding of skate takes time and is often 
uncertain. 
VOL. 54, PART 1. NEW SERIES. 
9 
