Phylum Nemathelminthes and Related Phyla 437 



symptoms appear. Allergic reactions are among the first effects to be 

 noted, and they appear in those persons who do not have microfilariae 

 in their blood. The most pronounced later effects are due to the 

 mechanical blocking of the lymphatic system. Due to this blocking, 

 lymph is diverted to the extremities, to the scrotum, or less commonly 

 to the arms, mammary glands, and the head region. This results in 

 tremendous enlargements of these regions, a condition known as ele- 

 phantiasis. Very little has been learned about the treatment of this 

 condition. Surgery does seem to help at times. 



Onchocerciasis. — In Africa, the Mexican states of Chiapas and 

 Oaxaca, and the Pacific slope of Guatemala, there is another human 

 filarial worm, Onchocerca. . The symptoms of Onchocerca infection 

 differ from those of Wuchereria inasmuch as the filariae accumulate 

 in tremendous numbers in the connective tissue just beneath the skin. 

 The embryos upon being released from the female pass into the blood 

 stream and collect in the connective tissue of the skin. Here they are 

 picked up by feeding black flies (Simuliiim sp.). Development occurs 

 in this fly which follows the same pattern as that of Wuchereria in the 

 mosquito. New hosts are also infected in a similar manner. The most 

 important effect of these parasites is that the adults gather in nodules. 

 These may be excised. In those cases of onchocerciasis in the New 

 World, the embryos often invade the optic nerve, cornea, and other 

 parts of the eye, producing blindness. 



The African Eyeworm. — Another worm with a very similar 

 life history is that known as Loa loa (141,£). This parasite lives in 

 the connective tissues of the skin of man and creeps about in response 

 to warmth. At times, they get in the conjunctiva of the eye. Often 

 there are swellings known as Calabar swellings. These last only a 

 few days and seem to be a local reaction to the release of the body 

 fluids of the worm. 



Dracunculus. — The last interesting human parasite to be con- 

 sidered here belongs to another group of the nematodes. The female 

 of this species, Dracunculus medinensis (141,D), attains a very large 

 size (2.5 to 4 feet), while the male is only 20 to 29 mm. in length. 

 These are found only in dry climates such as North Africa, Centfal 

 India, Egypt, and central Africa. The common name for this worm 

 is guinea worm and it probably is the "fiery serpent" of biblical 

 literature. 



