10 THE BLowF ies or NortH AMERICA 
presence of intrapostocular cilia, and the general structures of 
the male and female external and internal genitalia will separate 
the family Calliphoridae from all other Diptera now known to 
the author. The species of Sarcophagidae lack intrapostocular 
cilia and the general structure of the genitalia of both sexes 
indicate little actual relationship between the two families. These 
characters hold for all North American ecalliphorid and sar- 
cophagid species, and for all members of both families now 
known to the author. 
IMPORTANCE OF BLOWFLIES TO MAN | 
Blowflies have considerable effect upon the economy of man 
and are included among the insects of most importance to him. 
They may seriously affect the health of man and sometimes the 
health of his livestock. They also exert a distinct influence upon 
the abundance and welfare of wildlife due to their attacks upon 
animals and birds. Substantial sums are spent to alleviate 
certain conditions for which such flies are responsible and large 
expenditures are sometimes necessary for their control. 
TRANSMISSION OF DISEASES. The omnivorous and pro- 
miscuous feeding habits of many species of the more abundant 
blowflies enable them to be potential vectors of a number of 
diseases of man. The disease-carrying propensities of these flies 
are often overlooked. With the sole exception of the common 
housefly, the importance of the nonbiting flies is frequently 
neglected entirely. Blowflies may transmit pathogenic organisms 
to man by one or more of several methods. | 
Feeding upon infected filth such as human excrement or 
sewage, blowflies may easily infect food intended for human 
consumption and they may thus become of considerable 
importance during epidemics of intestinal diseases such as 
typhoid or cholera. Microorganisms may be transferred mechan- 
ically from an infected source to human food upon the appen- 
dages, body, hairs or bristles of blowflies which have fed or econ- 
gregated on infected materials. Flies which have fed upon 
infected materials may contaminate human food by the so-called 
‘“‘vomit-drop’’ or by depositing infected material on such food 
during defecation. 
Blowflies may become vectors of certain diseases because of 
their breeding habits and may be of considerable importance 
during epidemics of such diseases as plague and anthrax. The 
larvae of most species of blowflies occur principally in carcasses; 
animals dying from infectious diseases are ds readily blown as 
