182 Arthropods as Essential Hosts of Pathogenic Organisms 
Filaria immitis is a dangerous parasite of the dog, the adult worm 
living in the heart and veins of this animal. It is one of the species 
which has been clearly shown to undergo its development in the 
mosquito, particularly in Anopheles maculipennis and Aedes calopus 
(= Stegomyia). The larval form occurs in the peripheral blood, 
especially at night. When taken up by mosquitoes they differ from 
Filaria hancrofti in that they undergo their development in the 
Malpighian tubules rather than in the thoracic muscles. In 
about twelve days they have completed their growth in the tubules, 
pierce the distal end, and pass to the labium. This species occurs 
primarily in China and Japan, but is also found in Europe and in the 
United States. It is an especially favorable species for studying 
the transformations in the mosquito. 
Filar ice are also commonly found in birds, and in this country 
this is the most available source of laboratory material. We have 
found them locally (Ithaca, N. Y.) in the blood of 
over sixty per cent of all the crows examined, at 
any season of the year, and have also found them 
in English sparrows. 
In the crows, they often occur in enormous 
numbers, as many as two thousand having been 
found in a single drop of the blood of the most 
heavily infested specimen examined. For study, a 
small drop of blood should be mounted on a clean 
slide and the coverglass rung with vaseline or oil 
to prevent evaporation. In this way they can 
be kept for hours. 
Permanent preparations may be made by 
spreading out the blood in a film on a perfectly 
clean slide and staining. This is easiest done by touching the fresh 
drop of blood with the end of a second slide which is then held at 
an angle of about 45 0 to the first slide and drawn over it without 
pressure. Allow the smear to dry in the air and stain in the usual 
way with hematoxylin. 
Other Nematode Parasites of Man and Animals Developing 
in Arthropods 
Dracunculus medinensis (fig. 121), the so-called guinea-worm, is 
a nematode parasite of man which is widely distributed in tropical 
Africa, Asia, certain parts of Brazil and is occasionally imported 
into North America. 
121. Dracunculus 
medinensis; female; 
mouth; embryo. 
After Bastian and 
Leuckart. 
