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THE POPULAR SCIENCE MONTHLY 



their particular species, wbicli in many cases are the cause of peculiar 

 skin-affections. Since the presence of these animals constitutes the 

 disorder, it may be easily caught ; man may communicate it to the 

 domestic animals, and they may also give it to him ; it is only the 

 genus Sarcoptes^ however, that may be thus transferred from animals 

 to man. 



The true parasites just described, and many others. like them, are 

 nourished by the blood of their neighbors, but they never establish 

 themselves in the organs of their host, being free throughout their 

 lives. There is another class that live in freedom while young, but 

 when arrived at mature age, and the cares of a family are soon to be 

 assumed, they change in appearance, choose a host, and settle down 

 for life. The chigoe, a parasite of man in South America, is one of 

 these. It is only the female, however, that demands both lodging and 

 provisions, the male (Fig. 18) being contented with pillaging his vic- 

 tim as he passes by. It is a small species, which pierces the shoes and 

 clothes with its pointed beak (Fig. 19), and penetrates into the sub- 

 stance of the skin, generally selecting that of the toes. The male, as 



Fig. 18. Male Chigoe. 



Fig. 19. Head of Cuigoe. 



just remarked, takes his food and resumes his wanderings, but the 

 female seeks a hiding-place for permanent abode, and then grows to 

 such a monstrous size that the entire insect appears to be nothing 

 more than a mere appendage to the abdomen, as may be seen in Fig. 

 20, Besides man, this parasite infests the dog, the cat, the pig, the 

 goat, the horse, and the mule. 



Another form coming within this category, and the terror of trav- 

 elers on the coast of Guinea, is the Guinea-worm, Filarla inedinensis 

 (Fig. 21), also found in other parts of Africa, and said by Mitchell to 

 have been observed in South Carolina. It was long supposed that 

 this filaria could introduce itself into the cellular tissue of the body 

 directly through the skin, in the form of a microscopic embryo, but 

 several recent observers concur in the belief that it is transmitted by 

 means of the cyclops, a little fresh-water crustacean. This is swal- 

 lowed in drinking-water, and at the end of six weeks the presence 

 of the filaria is revealed by tumors, which later develop into open 

 sores, caused not by the worm itself, but by the dissemination of its 



