Arthropods and Man 
5 
occurs in the dog louse, or in the dog or cat fleas, and by accidentally 
ingesting the infested insect the vertebrate becomes infested. Simi¬ 
larly, Hymenolepis diminuta, a common tapeworm of rats and mice, 
and occasional in man, undergoes part of its life cycle in various meal- 
infesting insects, and is accidentally taken up by its definitive host. 
It is very probable that man becomes infested- with Dracunculus 
( Filaria ) medinensis through swallowing in drinking water, the 
crustacean, Cyclops, containing the larvae of this worm. 
2. By infecting man or animals on whose skin or mucous mem¬ 
branes the insect host may be crushed or may deposit its excrement. 
The pathogenic organism may then actively penetrate, or may be 
inoculated by scratching. The causative organism of typhus fever 
is thus transmitted by the body louse. 
3. By direct inoculation by its bite, the insect host may transfer 
the parasite which has undergone development within it. The 
malarial parasite is thus transferred by mosquitoes; the Texas fever 
parasite by cattle ticks. 
