SIPHONAPTERA. 229 



development of the human flea requires about a month 

 from the time the eggs are laid. 



In tropical countries, the flea which infests the rat 

 is very closely related to the human flea. This consti- 

 tutes a serious menace to the health of our sea-coast 

 communities. Rats are known to be distributors of the 

 bubonic plague in their own country; and rats crossing 

 the ocean from any of these countries, soon spread the 

 infection among the rats where they land. San Francisco 

 has had to fight this horror more than once. Unde- 

 sirable people are not the only undesirable things we re- 

 ceive from foreign shores. 



