68 
The Genus Leucocytozoon 
in the life cycle of the leucocytic parasite of mammals and the haemo¬ 
gregarines of cold-blooded animals is discovered there is no reasonable 
course open but to include them in the same genus. 
Miss Porter states that “ The Leucocytozoa of mammals are very 
similar in general morphology to the Haemogregarina found in the red 
blood corpuscles of certain mammals” but she continues “surely the 
difference in habitat is sufficiently striking to separate the genera of 
strict mammalian Haemogregarines and Leucocytozoa.” It is difficult 
to understand how mere habitat alone can in any way be converted into 
a generic character. In this, Miss Porter follows James and Patton who 
are stated to have the advantage, over Laveran and Mesnil,of first-hand 
knowledge of the group. Apparently Miss Porter imagines that Laveran 
and Mesnil and possibly others have not this first-hand knowledge, but 
I can assure her that in this she is mistaken. 
In his paper on the leucocytic parasite of dogs James remarks 
“while it undoubtedly has affinities with the haemogregarines the fact 
that it is parasitic upon the leucocytes and that it represents a hitherto 
entirely unknown form of mammalian blood-infection would seem to 
justify its recognition as the type of a new genus,” and Patton at the 
close of his description of the leucocytic parasite of the palm-squirrel 
makes this assertion, “It will be seen that the description of this 
parasite agrees in every detail with that of a haemogregarine.” In 
spite of this complete agreement Patton regards the parasite as 
belonging to a distinct genus presumably because it is within a leucocyte. 
The question resolves itself into this—Can mere habitat be regarded as 
a generic character to separate one parasite from another when in other 
respects there is “agreement in every detail ”? 
It is very difficult to understand Patton’s attitude towards his two 
groups Haemamoebina and Haemogregarina. In the genus Haem- 
amoeba are included the malarial parasites of man the life cycles of which 
are so well known, the similar parasites of birds ( Proteosoma), the 
Halteridium of birds which differs very much from the malarial parasites 
both in their asexual multiplication and mode of transmission and 
finally in this same genus he prefers to include the Leucocytozoon of 
birds though it displays such marked differences from the pigmented 
malarial parasites. A grouping together in a single genus of such 
diverse forms is a view accepted by very few authorities. If one 
compares such a parasite as the pigmented benign tertian parasite of 
malaria with a Leucocytozoon of a bird one can see at a glance that 
they are quite distinct. 
