2IO THE ANIMAL PARASITES OF MAN 



their head on to the appendices of the pylorus of fishes ; other 

 species (Hymenolepis diminuta) occasionally fix their heads in 

 the ductus choledochus, and this is more frequent still in the 

 tapeworms of the Hyrax, which occasionally penetrate entirely 

 into the biliary ducts. [Dr. Theiler of Pretoria has sent me a new 

 tapeworm which invades the liver of sheep in the Transvaal. F.V.T.] 



In the diseases of sheep induced by cestodes, the worms have 

 been observed also in the pancreas. Specimens found in the 

 large intestines were probably being evacuated. 



The cestodes are looked upon as fairly inert creatures ; this 

 opinion having been formed by observing their condition in the 

 cold cadavers of warm-blooded animals. Actually, however, they are 

 exceedingly active and accomplish local movements within the 

 intestine, for they have been found in the ducts communicating 

 with the bowel, or in the stomach, and may even make their 

 way forward into the oesophagus. 



They also invade other abdominal organs through abnor- 

 mal communications, or through any that may be temporarily open 

 between the intestine and such organs ; they thus reach the 

 abdominal cavity or the urinary bladder, or they work their way 

 through the peritoneum. 



They produce changes in the intestinal mucous membrane at 

 the place of their attachment, the alterations varying in intensity 

 according to the structure of the clinging organs. The mucous 

 membrane is elevated in knob-like areas by the suckers ; the 

 epithelial cells become atrophied or may be entirely obliterated. 

 Dipylidium caninum bores into the openings of Lieberkuhn's 

 glands with its rostellum, dilating the lumen to two or three 

 times its normal size, while the suckers remain fixed between the 

 basal parts of the .cells. Species with powerful armatures pene- 

 trate deeper into the submucosa, and some that are not pro- 

 vided with exceptionally strong armatures or are even unarmed, may 

 be actually found with the scolex embedded in the muscles of the 

 intestinal walls or even protruding beyond (Tania tetmgona, Mol., in 

 fowls, &c.). Other species, again, even cause perforation of the 

 walls of the intestine of their hosts. 



THE LENGTH OF LIFE OF THE ADULT TAPEWORMS certainly 

 varies ; as a rule it appears to last only about a year ; in" other 

 cases (Ligula) it averages only a few days, but we are likewise 

 aware that certain species of cestodes of man attain an age of 

 several or many years (thirty-five). The natural death of -ces- 



