ON THE TRYPANOSOME OF THE LITTLE OWL. 
181 
occurs in the gametocyte phase, i. e. in the character of male 
or female individuals which give rise only to the sexual 
elements. Moreover, we have never found any corresponding 
sexual difference among the massive trypanosomes which might 
indicate that they were of male or female character. They 
never show the marked differences in staining reaction pre- 
sented by the Leucocytozoon. 
We may repeat, therefore, that ‘ ‘ T . ziemanni” is to be 
regarded only as a phase or type of form of T. noctuae, just 
as similar large forms occur in T. f ringillinar um; and 
again, for instance, in the trypanosome parasitic in Eury- 
stomus afer (allied to the roller-bird), where they are also 
regarded by Zupitza (loc. cit.) as “ Leucocy tozoon - 
forms 99 and designated “T. ziemanni ”! 1 
In view of the general agreement which we have found 
between the different types of T. noctuae and those of T. 
f ringillinarum, why, it may be asked, do we not regard 
both these parasites, for instance, as belonging to the same 
species? We feel practically certain that they are quite 
distinct forms for the following reasons : First, on the 
ground of their occurrence in very different birds, the hosts 
being respectively little owls (and perhaps also other owls), 
and chaffinches (and also redpolls and perhaps other Frin- 
gillinae). Secondly, we have on several occasions inoculated 
a little owl, free from any blood-parasites, with cultural forms 
of T. frinfifillinarum , but have been unsuccessful in obtain- 
ing any development of the trypanosomes in the bird. Lastly, 
on morphological grounds, the various types of form of T. 
noctuae appear to attain a slightly but distinctly larger size 
than do the corresponding types of T. fringillinarum 
so far as we can judge from our own observations. This 
is seen from the following table comparing the two sets of 
forms : 
1 In any case, it is most unlikely that this parasite, occurring in a 
quite different bird, would be the same species as Scliaudinn’s “ T. 
zeimanni .” 
