152 
E. A. MINCHIN AND H. M. WOODCOCK. 
recognised, we think, as constituting a perfectly definite 
phase in the life-history of these Avian trypanosomes. As 
above mentioned, the parasites were observed living in the 
peripheral blood on two occasions, in the night-time ; only 
very few trypauosomes were noticed altogether in several 
cover-slip preparations. They belonged to one type, and 
were fairly small and stumpy, spindle-like or rather broad ; as 
will be seen later, these forms are not quite comparable to 
those of the third category above described. All the trypano- 
somes observed living in this owl, whether in the blood or 
(later) in the bone-marrow, were free ; none showed any 
inclination to become attached to any cell. 
To sum up : In spite of many and long-continued observa- 
tions we never succeeded in seeing any form of the trypano- 
some of the little owl either penetrate into, or become 
completely attached to a cell, and lose concurrently its 
locomotor organs ; and this notwithstanding 1 that both 
Halteridia and Leucocytozoa were present in all cases in the 
same birds. The only manner in which we observed the 
trypanosomes to be associated with cell- elements was that of 
their attachment by one extremity — which might be, appa- 
rently, either end indifferently; and we never saw this 
attachment develop into any closer connection (cf. however, 
below, p. 165). 
B. Leucocy tozoon. — We do not intend in this paper to 
discuss the minute structure of these parasites, but only to 
note certain features observed, and more especially those 
bearing upon the question of the actual connection of these 
intra-cellular parasites with the trypanosomes. Owl 11 had 
a good infection of Leucocytozoon and was the most 
suitable of the earlier birds for studying this form. The 
parasites were all in the gametocyte-phase, most of them 
being nearly full-grown in size. In nearly all the host-cell 
had acquired the characteristic spindle-like appearance, with 
the cytoplasm drawn out in two long, tapering processes. 
The degree of plumpness of the parasites varied slightly ; 
some were more slender, others rather stouter ; but apart from 
