SUMMARY. 
Hepatozoon perniciosum, n. g., n. sp., is a hsemogregarine found in 
white rats in Washington, D. C., and the cause of an epizootic 
observed among these animals. The protozoon is conveyed by a mite 
{Lelaps echidninus Berlese), which is the true intermediate host. 
Infection is transmitted to the rat when the mite is swallowed by 
the rat. 
The mites are ecto-parasites upon the rats, from which they 
receive infection by sucking the blood. 
Multiplication of the haemogregarine in the rat takes place in the 
liver. In the stomach of the mite the hsemogregarines conjugate 
and form an ookinet, which penetrates the stomach wall and com- 
pletes its development in the body tissues of the mite. 
The illustrations in this bulletin have been prepared from draw- 
ings made by the laboratory artist. Prof. Leonard II. Wilder. 
( 6 ) 
