0. M. Wen yon 
6T 
7. The parasites are devoid of pigment, they are not enclosed in 
any cyst, they never leave the host-cell to move about in the blood 
plasma as do the haemogregarines, the asexual mode of reproduction is 
unknown nor is there any knowledge of the further development of the 
zygote and of the mode of transmission. 
Such are the characters of the Leucocytozoon of birds. It will be 
evident to anyone who knows the group that its nearest relative is 
Haemoproteus (Halteridium) of the same host. It differs from 
Halteridium however in its large size, the absence of melanin pigment 
and the peculiar action it has upon its host-cell. It will be equally 
evident that it has no connection with the haemogregarines nor with 
the closely allied leucocytic parasites of mammals though Miss Porter 
would group the latter with the avian parasites. 
The characters of these leucocytic parasites of mammals are as 
follows:— 
1. They are parasitic in leucocytes of mammals. 
2. They do not alter the shape of the host-cell to any extent 
though they may cause considerable change in its nucleus. 
3. There is no sexual differentiation to be compared with that 
existing in the bird-parasites. 
4. The nucleus is characteristic and resembles that of haemogre¬ 
garines. It is quite unlike the nucleus of the Leucocytozoon and in staining 
reaction approaches that of the nucleus of the host-cell. 
5. A cyst (cytocyst) is frequently though not invariably present. 
Within the cyst the parasite lies as a cylindrical body completely 
filling the cyst or as an elongate vermicule doubled upon itself in the 
shape of a U. 
6. The parasites may leave their host-cell and their cyst and move 
about in the plasma as minute gregarines. 
7. Asexual multiplication is by schizogony in a cell of some 
internal organ. 
8. Sexual development has only been completely described in one 
case namely in the case of the leucocytic parasite of the rat. It has 
also been described but less completely for the similar parasite of dogs. 
It is quite clear that these parasites are very closely allied to the 
haemogregarines and far removed from the Leucocytozoon of birds. 
Indeed if we look into these characters just enumerated were find there is 
not a single one of them which may not be applied to some typical 
haemogregarine. The fact that the host-cell is a leucocyte can hardly 
be regarded as a generic character and unless some marked difference 
5—2 
