PARASITISM 315 



importance, since means of inhibiting the 

 multiplication or development of the flies will 

 go far in lessening the incidence of these de- 

 structive maladies. 



In the same manner mosquitoes have been 

 shown not only to be optional parasites them- 

 selves, but also to act as definitive hosts of 

 other parasites that they transmit from indi- 

 vidual to individual. Such parasitic diseases 

 of man as paludism or malaria, yellow-fever, and 

 filariasis are thus transmitted and suspicions 

 are abroad that other diseases may be similarly 

 spread. 



It was only through intelligent understanding 

 of the relation of the mosquito to yellow fever 

 that permitted the eradication of the disease 

 from Havana and Panama. 

 Dipterous insects are also important plant 

 parasites sometimes penetrating the tissues in 

 the larval state to complete their metamorpho- 

 sis, sometimes stinging the plant during ovu- 

 lation and causing the formation of galls or 

 tumors upon the tissues of which the larvae live. 

 Order Siphonaptera. This order includes the 

 fleas, of which there are many species peculiar 

 to different animals, though occasionally in 

 case of necessity feeding promiscuously upon 

 warm-blooded creatures. The symbiotic rela- 

 tionship varies in closeness in different cases. 

 Upon hairy animals the fleas remain in more 

 intimate association than upon man. The 

 fleas have a disposition to leave the host occa- 

 sionally and hop about the ground, perhaps to 

 find new hosts. The parasitic life only apper- 

 tains to the adult stage, the larval and pupal 

 stages occurring upon the ground where vege- 

 table food is consumed. One flea, the Sarcop- 

 sylla penetrans, is peculiar in that the female 



