45 
by Neveu-Lemaire and advocated by Liihe divides the Hsemogregari- 
nidde into three genera, as already mentioned. 
In view of the restricted knowledge of many of the parasites of this 
general group, and especially in view of the fact that the complete 
life cycle for so few forms is definitel}^ established, considerable diffi- 
culty naturally arises in attempting to definitely classify Hepatozoon 
perniciosum, the organism under discussion. As Liihe, who has 
recentl}^ published a re visional discussion of this group, has classified 
an apparently rather closely allied species, namely, Hxmogregarina 
balfouri, from Jaculus jaculus in the family Hsemogregarinidse, it 
seems best to place this new species for rats at least provisionally in 
the same family. 
In attempting to classily the organism in one of the new genera 
we are faced by two dangers: In the majority of the species of this 
group the complete life C 5 "cle has not yet been established. If, now, 
the organism under discussion is classified in one of these new genera 
the danger is present of giving a total misconception to the life cycle 
of the other forms. If, on the other hand, a new genus is proposed 
for this species the danger is present that when the life cycle of the 
other species of this group shall become known this new genus will be 
shown to be unnecessary. A choice must therefore be made between 
running the risk of confusing the biology of species with which the 
present parasite ma}^ have no tiring whatever to do and of unneces- 
sarily creating a new s^^stematic name. When these considerations 
are weighed it would appear that it is much more difficult to correct 
a biological confusion than it is to suppress a synonym. On this 
account it is believed that the lesser of the two evils lies in proposing 
for the species under discussion a new generic name. Dr. Charles 
Waddell Stiles, chief of the division of zoology. Hygienic Laboratory, 
Public Health and Marine-Hospital Service has suggested the provi- 
sional formation of a new genus. The writer accepts this view, and 
accordingly proposes Hepatozoon, kindly suggested by Doctor Stiles 
as the new mono-typic genus, with Hepatozoon perniciosum as type 
species. 
As only one species is at present established for this genus it is 
naturally difficult to separate the generic from the specific characters. 
As diagnosis for Hepatozoon perniciosum n. g., n. sp., the following 
may be given: 
In the Rat. 
When an infected mite is swallowed by a rat the sporocysts are acted 
upon by the digestive juices and the sporozoites are liberated. The 
sporozoites become actively motile striated vermicules measuring 
16 by 4 micra. They penetrate the intestinal villi of the rat, enter 
