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1906] OLIVE—DEVELOPMENT OF EMPUSA 193 
BREFELD (’70, "71, 77), however, was successful in transmitting 
the parasite through external inoculation of spores, and he found 
that in the case of Empusa muscae infection took place only through 
the thinner whitish parts of the skin on the under side of the fly’s 
body; whereas in another species, E. sphaerosperma, the infected 
hyphae gained an entrance at any part of the skin of the cabbage 
larva. This author has contributed more on this point than any 
other, in that he was able to germinate the conidia in artificial 
media as well as on the surface of the insect body, and to find with 
the microscope the germinating hyphae actually boring through, the 
skin of the host. In his series of articles, BREFELD has described 
the complete course of development of two species of Empusa, E. 
muscae Cohn and E. sphaerosperma Fres., which furnish quite differ- 
ent types of vegetative growth. According to him, in E. muscae there 
are formed from those germ-tubes which have penetrated into the 
body-cavity of the insect numerous detached non-nucleate cells, 
which reproduce by repeated yeast-like sprouting, and which grow 
within the fat-bodies of the host. At a certain advanced stage of the 
development of the fungus, the reproduction of the cells by budding 
ceases, and each grows at one or both ends into a long unbranched 
tube, which grows through the body-wall and produces at its external 
end a single conidium. In the other species, E. sphaerosperma, 
BREFELD found that the germ-tube produces, on the other hand, a 
copiously branching mycelium with many cross-partitions, which 
finally fills the body-cavity of the host. At the end of the vegetative 
period, this mycelium sends out hyphae which grow to the surface, 
branch digitately, and finally produce acrogenously at each ultimate 
end a single conidium. 
Em pusa sphaeros perma further differs from E. muscae in producing 
resting spores. COHN (’55, p. 343) had already suggested, since he 
could not make the conidiospores of E. muscae germinate, that per- 
haps the conidia themselves required a year of rest. But BREFELD 
(°70, ’71), proved conclusively that the spores of this form were short- 
lived, living only for a few days; hence his first suggestion in regard to 
the puzzling question as to the wintering of such a species was that 
this form was probably heteroecious, and that resting spores were pro- 
duced in some other host. Later, however (’84, p. 68), he seems 
