ANIMAL PARASITES IN THE INTESTINES 155 



larval form and the adult tapeworm. Usually the cyst 

 is found in one animal host and the tapeworm in another. 

 The hosts are usually not even of the same species. As an 

 example, the tapeworm Taenia coenurus has for its host the 

 dog, while the larval stage, the Coenurus cerebralis, has for 

 its host usually the sheep. The Taenia cucumerina, the 

 common tapeworm of the dog in its cyst form, is harbored 

 by the common dog flea (Pulex serraticeps) . ' 



The development of the tapeworm is as follows : The eggs 

 with the segments of the adult worm which inhabits the 

 intestines are voided with the feces and thus reach the out- 

 side world. There they are taken up by a second host, in 

 the stomach of which the embryo, often provided with 

 hooks, is hatched. These embryos penetrate the bowel 

 wall and enter the bloodvessels, and are carried to distant 

 organs, such as the muscles, brain, lungs, etc., developing 

 in these organs cysts. If organs containing such cysts are 

 ingested by animals which would form the proper host 

 there develops in the intestine a tapeworm. The tapeworm 

 is provided with a head or scolex to which is attached a 

 number of segments or colonies that, when ripe, contain the 

 fertile egg of the tapeworm. 



Varieties. — ^Each of the domesticated animals has species 

 of tapeworms peculiar to itself. 

 Horse: 1. Taenia perfoliata. 



2. Taenia plicata. 



3. Taenia mamillana. 

 Ox: 1. Taenia expansa. 



2. Taenia denticulata. 



3. Taenia alba. 

 Sheep: 1. Taenia expansa. 



2. Taenia ovilla. 



3. Taenia alba. 



4. Taenia fimbriata. 



Symptoms.— Tapeworms, unless present in large numbers, 

 rarely produce symptoms. For instance, over 50 per cent, 

 of the dogs harbor tapeworms, particularly the Taenia cucu- 

 merina. On the other hand, tapeworms sometimes cause 

 chronic intestinal catarrh (diarrhea alternating with con- 



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