154 
E. A. M INCHIN AND H. M. WOODCOCK. 
An interesting feature wliich may be pointed out was the 
variation we noticed, both in the number of gametocytes 
present in the drops of blood examined and in the apparent 
ripeness at different times. Mathis and Leger (9) have 
remarked on the occurrence of what they describe as a 
periodicity of the gametocytes in the circulating blood, which 
they noticed on two occasions in Leucocytozoon caul- 
leryi, of fowls in Tonkin. The parasites would be observed 
for a certain number of days (four to seven) in varying 
frequency, and then would apparently disappear from the 
blood and not be seen again, often for some weeks. In the 
cases instanced there appeared to be no regularity either 
about the length of time during which the parasites were not 
observed, or about the period, usually a few days, when they 
were present. 
We never observed in any of our owls infected with 
Leucocytozoon a complete disappearance of this parasite 
from the blood. The following notes illustrate the variation 
to which we have just alluded in owl No. 11. 
March 18th, morning after arrival: Leucocytozoon 
present ; parasites frequent. 
March 19th-20th, midnight : Parasites distinctly more 
numerous, approaching abundance. Many rounded-off forms 
(i.e.ripe females, which had ruptured the host-cell) seen. 
Probably ripe male individuals were also present, though no 
flagellating forms were actually seen. 
March 23rd, morning: At first no signs of Leucocyto- 
zoon, but after some searching the parasites were found. 
They were infrequent to scanty, only five or six individuals, 
one of which was rounded-off, being noticed in four cover- 
slip preparations. 
March 23rd-24th, midnight : Parasites numerous. In a 
cover-slip preparation of pure blood only spindle-shaped, 
intra-cellular forms were seen; but in a preparation to which 
a drop of salt-citrate solution had been added, many 
liberated females and some flagellating male gametocytes 
were found. 
