i82 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 bancrofti 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. 



FilaricB are also commonly found in birds, and in this country 

 this is the most available source of laboratory material. We have 

 foimd 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 fovind them 

 in English sparrows. 



In the crows, they often occtu 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 



121. Dracunculus , ^ j, - 



medinensis; female; be kept lOr hOtlrS. 



After iastian and Permanent preparations may be made by 



spreading out the blood in a film on a perfectly 

 clean sHde and staining. This is easiest done by touching the fresh 

 drop of blood with the end of a second sHde which is then held at 

 an angle of about 45° to the first sHde and drawn over it without 

 pressure. Allow the smear to dry in the air and stain in the usual 

 way with hsematoxylin. 



Other Nematode Paeasites op Man and Animals Developing 



IN Arthhopods 



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. 



