ON THE TRYPANOSOME OE THE LITTLE OWL. 161 
endeavour to become free. This movement went on for- 
about three quarters of an hour, but with no success. 
The free microgametes themselves were, as already men- 
tioned, very slender thread-like bodies ; they were, it any- 
thing, rather longer than those of Halteridium. The 
gametes, living, were observed very closely, but no signs of 
any undulating membrane could be made out; nor could any 
more active, whip-like part of the body, corresponding to a 
free flagellum, be distinguished. Unfortunately, we have 
not been able to find any microgametes in our permanent 
preparations; Wenyon, however, has figured ( 17 ) the male 
elements of L. neavei, from a stained preparation, and these 
also appear simply as threads. It is most likely, we think, 
that the minute structure of the microgametes of Leucocy- 
tozoon is very similar to that of the corresponding elements in 
Halteridium ; in the latter parasite, the male gamete, as has 
been described by one of us (loc. cit.), consists of a delicate 
cytoplasmic thread, containing two or three chromatic masses 
of varying size and having a distinct centrosomic granule at 
one extremity (cf. also below). 
c. Halteridium. — Three of our owls had a good Halteri- 
dlal infection, Nos. 13, 19, and 23; the parasites were 
plentiful in the first, abundant in No. 19, and simply swarm- 
ing in No. 23. It may be remarked here that the terms 
“ numerous,” “abundant,” and so on, as we have used them, 
do not mean the same thing, as regards the actual number of 
the parasites present in the case of Halteridium and 
Leucocy tozoon respectively; this will be understood 
when the different habitat of the two forms and the relative 
proportion of red blood-cells to small mononuclear leucocytes 
is borne in mind. For instance, we may consider Leuco- 
cytozoon to be numerous when two or three individuals on 
an average can be seen in a single field of a fresh cover-slip 
preparation, working with a dry lens (obj. D or 4 mm. apochro- 
matic); but we should not regard Halteridium as abundant 
in an infected bird unless on an average at least one or two 
individuals occurred in a single field of a stained smear, 
