102 I'ROTECTION OF PLANTS, 1916-17 



the Nematoda, which includes by far the major part, and the Acanthoce- 

 phala, which are characterized by the possession of a protrusible proboscis 

 covered with many rows of recurved hooks. Without attempting to limit 

 our discussion to the most important parasites of man, we shall select a few 

 readily available forms to emphasize typical life histories. 



The Trematoda, or flukes, we may dismiss with scant attention, for 

 they are relatively unimportant for both man and the higher animals in this 

 country. Imported cases of human infestation have been occasionally re- 

 ported for the United States. Immediately following the World's Fair in 

 Chicago, in 1893, a group of Boer soldiers, who had been on exhibit on the 

 Midway, toured the United States. Examination showed that several oi 

 these men harbored the blood fluke Schistosoma haematabium. I have found 

 the related species, Schistosoma mansoni, in aPortoRican student at Ithaca, 

 N.Y., and there are several other records of its occurrence in the United 

 States. My assistant, Mr. W. L. Chandler, and I have found concurrent 

 infestation with two liver flukes, Clonorchis sinensis and Opisthorcis felineus^ 

 in a Japanese student. The lung fluke, Paragonimus westermanni, .has 

 similarly been found in this country in Japanese, Coreans, and Chinese. It 

 is more than possible that some of the trematode parasites of man will ulti- 

 mately become established in this country. 



The Cestoda, or tapeworms, almost without exception must infest two 

 different species of animals in the course of their life hisotry. The asexual 

 stage is developed in an intermediate host which, typically, is preyed upon 

 by the primary host, in which the sexual stage of the worm must develop. 

 Thusi, to know the origin of a tapewomi which we find in its mature state in 

 an animal, we must study the food of the host and, as we shall.see, the ecto- 

 parasites which attack it. 



A good illustration of this life cycle is afforded by a very common tape- 

 worm of cats. Taenia crassicollis. The immature stage occurs as a round, 

 cream-colored cyst about the size of a pea in the liver of mice (fig. 1), rats, 

 and certain other rodents. Within the cyst is the head of the future tape- 

 worm, wit^ a body one-half inch or more in length (fig. 2).' When the 

 infested mouse is eaten by a cat, the cyst and the body of the larval form are 

 digested, the head attaches to the intestinal mucosa and the adult tape- 

 worm promptly develops. The specimen before you was secured by feeding 

 infested rat liver to a young kitten, free from other intestinal parasites, and 

 the mature worm was recovered in a little over six weeks' time. Ripe seg- 

 ments filled with eggs are passed by infested cats, the eggs are scattered and 

 taken up by mice and other rodents, and these in turn develop the cysts and 

 become capable of passing on the parasite to their hereditary enemy, the 



