318 
act as hosts, at the time when the parasites would be passed out to the 
outer world. For the hibernating females have first to develope and 
ripen their eggs, which have to be laid and undergo further development, 
before there can be any larvae about. One of the first things a hiber- 
nating female does, on waking up in the spring, is to have a meal of 
blood; for the eggs of Culex pipiens will not develope without blood, of 
this I have assured myself. Undoubtedly, after a female had partaken 
of blood, a large number of the parasites would be passed out to the 
exterior with the first faecal evacuations, for some faeces are evacuated 
very soon after a meal, especially if the mosquito has gorged herself. 
So far as can be seen, therefore, a great proportion of the parasites must 
perish. Before I knew of the occurrence of cysts, it seemed to me that 
it was not by the expulsion of the Flagellates that the survival of the 
species was ensured; and, as will be mentioned below, another mode of 
dispersal appeared possible. Now, however, that I have found that en- 
cystment does take place, it appears probable that the cysts are destined 
to infect larvae. Nevertheless, even if this is the case, the chances 
against successful larval infection seem to be very great. This is shewn 
by the following fact. After the females had all disappeared from his 
cellar, Mr. Bacot placed receptacles containing water in his garden, for 
the larvae to develope in. He brought me up numbers of larvae, of 
different ages and certainly from different broods, at intervals from 
these receptacles. All the larvae, without exception, were of Culex 
pipiens. I examined a number and not in a single case have I seen any 
signs of a Flagellate, whether in the active or resting condition; and it 
may be reasonably supposed that some of these larvae, at any rate, were 
the offspring of one or more of the infected females. I may also repeat 
here, what I have noted on several previous occasions, that I must by 
now have examined altogether hundreds of larvae and newly emerged 
imagines, both male and female, of C. pipiens, from various sources 
within a short distance of each other in this same locality, during the 
last few years, without ever coming upon a Flagellate! 
Having regard to the observations recorded above, there are one 
or two tentative possibilities bearing upon the subsequent history of 
these flagellate parasites which should not, I think, be overlooked. 
And this brings me to a subject which I wish to discuss shortly, namely, 
the question of the connection or otherwise of “Crithidia” fasciculata 
with some Trypanosome. Culex pipiens is essentially the British mos- 
quito which likes Avian blood; à propos of this point, I may mention 
that a week or so after Mr. Bacot brought me the last hibernating fe- 
males, he captured an individual in his garden which contained fresh 
blood. This I examined and found to be Avian blood. Now one possi- 
