156 ROLAND THAXTER ON THE 



usual host (^Musca domostica) ; siuce, if not indigenous in remote localities, its transpor- 

 tation by sea would be ahnost inevitable. As a rule, the species is found about houses, 

 usually within them, occuri-ing in great abundance from the latter part of June until late 

 in the autumn; yet its occurrence out-of-doors is an exceptional phenomenon and has 

 been noticed in only a few cases. This is the more singular, since hosts that are liable 

 to infection are very common in the open air, and a transmission to them of the dis- 

 ease from the house-fly would seem a very easy matter. Isolated examples of E. Muscae 

 are, however, almost never found in situations frequented, for instance, by Syrj^hus flies, 

 although Gornu^ records an extensive epidemic in which the hosts attacked belonged 

 to this genus. In my own experience I know of only two instances of the isolated oc- 

 currence of this species out-of-doors. The first was observed early in July on Mt. 

 Washington where two small specimens of Syrplias were found on bushes in the alpine 

 region, both of which were infested by JS. Muscae; and in the second instance a speci- 

 men of a small, yellow-bodied Syrphus was found at Albany in August on the flowers 

 of SoUdago by Mr. A. F. Chatfield, and forwarded to me, the host in this case being at- 

 tacked by the same Empusa. Mr. Chatfield infonns me that it was the only specimen 

 observed, and although I have searched with great care for similar sj^ecimens, I have 

 never seen a second instance of the kind. An epidemic in the open aii-, caused by E. 

 Muscae, I have, however, observed in one locality where a hairy black fly {AidJiomyia sj).) 

 about as large as M. domestica, was found killed by this fungus. This locality was the 

 region in the immediate vicinity of the snow arch at the head of Tuckerman's ravine, 

 on Mt. Washington, where the affected flies occurred sticking in large numbers to the 

 flowers of SoUdago and Ileracleum. These flowers were also visited by an abundance 

 of other flies, among them many examples of the same species of Syrphus previously 

 mentioned from Mt. Washington and Alban}^; but in no instance did I find one of these 

 or of the numerous other Syrphidae and Muscidae visiting the flowers, that showed 

 any signs of infection from the black flies with which they could hardly have failed to 

 come in contact. This faiUxre of certain species to contract the disease, although known 

 to be subject to it, is interesting as indicating that even a slight change of hosts among 

 Empusae is often difficult, until the fungus has become established to some extent in its 

 new conditions, and may go far to explain the difficulty expei-ienced in cross infection 

 subsequently mentioned under E. Grylli and E. sjihaerosperma. 



The species is readily distinguished by its pointed, bell-shaped, spores which, although 

 entirely simihir to those of E. Cidicis, are much larger. The probable rupture of the col- 

 umella has been previously alluded to (p. 141) and the surrounding pellicle of proto- 

 plasm gives a characteristic appearance to spores which, for example, have been discharged 

 upon a glass slide (figs. 5-6). One of the chief points of interest about the species is 

 the uncertainty that exists concerning its resting spores, which, although the form is so 

 universal have as yet been observed in only one instance. Winter''^ states that he discov- 

 ered specimens of 3f. domestica in-doors which contained resting spores, and also pro- 

 duced conidia which he identified as belonging to E. Muscae. It seems quite impossible 

 that Winter should have mistaken the conidia of any other species for those of ^. Mus- 

 cae J jQt this observation, although referred to, is not credited by Brefeld, who concludes 



' I. c. B. = I. c. 



