ON THE TRYPANOSOME OF THE LITTLE OWL. 
179 
may develop further into larg'e “blue” forms; these were 
found in the general circulation in the autumn in the case of 
T. frin gillinarum . 
The chief, and, indeed, about the only point of difference 
between the trypanosome of the little owl and T. fringil- 
linarum, so far as we have observed the two parasites, is 
that in the latter species the massive forms were not found in 
association with the small forms and the medium-sized 
(“definitive”) individuals in the early spring, as in the 
former parasite. It is quite possible, however, that these 
forms could be found at that period in T. frin gill inarum 
also. 1 Hence we do not now consider that there is much to be 
gained by continuing to distinguish the medium-sized slender 
individuals as “ definitive ” forms. In the case of the owl- 
trypanosome this phase does not appear to be so prominent or 
persistent as was found to be the case in T. frin gilli- 
narum. It was mentioned in describing that species that 
the “ordinary” forms, as they were regarded, might pass 
later into the massive “ blue ” type. As we have shown above 
in the present case there is undoubtedly a transition from 
medium-sized slender forms to the large bine type ; though 
we are uncertain whether the former phase in its most fully 
developed condition (cf. figs. 7 and 8) undergoes this 
further development. 
From the marked correspondence as regards the different 
types of form which we have found in the case of two species 
from widely different hosts we venture to think that the 
scheme drawn up on p. 17G may be regarded as applicable in 
the main to other Avian trypanosomes, and may perhaps be 
taken as indicating typical phases in the life-cycle occurring 
in the bird which are common to most species. Heading 
Zupitza’s paper in this light we find that several points of 
agreement with our results are shown by the parasites with 
which he worked. The same types of individual are described 
1 Since this paper was sent to press, one of us (H. M. W.) has found 
these large forms in a chaffinch infected with I. fringillinarum early 
in May. 
