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A MICROFILARIA {MICROFILARIA ROSENAUI N. SR FROM 
THE CALIFORNIA GROUND SQUIRREL {CITELLUS 
BEECH EYI). 
By GEORGE W. McCOY, 
Passed Assistant Surgeon, United States Public Health and Marine- 
Hospital Service. 
{From the Federal Laboratory, San Francisco, California.) 
With Plate VII. 
The following is a brief description of a blood worm which was first 
observed by Mr J. W. Kehoe, one of the technical assistants at the 
Federal Laboratory. The parasite has been found in squirrels coming 
from almost all parts of California east of the Sierra Nevada Mountains, 
and between the Mexican border and the Sacramento River (between 
33° and 38° North Latitude). 
Rodents from the southern sections of the State seem to show a 
higher percentage of infestation than tliose from further north. It is 
probable that at least five per cent, of the squirrels from the part of 
the State in which the parasites are found harbour the worm. There 
is no evidence that the nematode exercises any deleterious influence on 
the host. The adult forms of the parasite have not been found though 
careful search for them has been made. 
Description of the worm : In the fresh blood attention is attracted 
to the parasite by a movement among the cells, and careful inspection 
shows this to be due to a very active worm. While the movements are 
quite vigorous no definite progress is made. The worm has been found 
alive two or three days after the death of the host. There is no 
evidence of the presence of a sheath. The tail is gently tapering while 
the head is rather blunt. The structure of the parasite cannot be 
studied satisfactorily in fresh preparations. The worm is readil}^ stained 
by the ordinary basic dyes, but, for the study of the structure, Giemsa’s 
method has given the best results. There is a faintly staining cuticle 
