CESTODES : GENERATIVE ORGANS 205 



duction of mature proglot tides or of the .fully developed ova of 

 Tcenia crassicollis (of the cat) into the stomach of mice, the 

 oncospheres escape from the shell in the middle portion of the 

 small intestine, and a few hours later penetrate into the intestinal 

 wall by means of a boring movement ; they have been found in 

 this position twenty-seven to thirty hours after the infection. By 

 means of this migration, for which purpose they employ their 

 hooks, they attain the blood-vessels of the intestine, indeed, already 

 nine hours after the infection and later they are found in the blood 

 of the portal vein, and in the course of the second day after infection 

 they are found in the capillaries of the liver, which this species does 

 not leave. 



Leuckart, in experimental feeding of rabbits with oncospheres 

 of Tcemia serrata (of the dog), found free oncospheres in the stomach 

 of the experimental animal, but not in the intestine ; however, 

 he came across them again in the blood of the portal vein. The 

 way through blood-vessels to the liver is the normal path for 

 those species of Taenia, the offspring of which become cysticerci in 

 mammals ; and this, even in those cases in which the oncospheres 

 develop further in the omentum or in the abdominal cavity (Cysti- 

 cercus tenuicollis, C. pisiformis), for here also distinct alterations are 

 observable in the liver, that lead one to the conclusion that there 

 has been a secondary migration out of the liver into the abdominal 

 cavity. Indeed, one must not imagine that the young stages of 

 the cestodes are absolutely passive ; once they have invaded an organ 

 they travel actively, and leave distinct traces of their passage. 



In other cases the oncospheres leave the liver with the circula- 

 tion, and, are thus distributed further in the body ; they may 

 settle and develop in various organs, or they may only do so 

 in certain organs. Many oncospheres may, by travelling through 

 the intestinal wall, penetrate through it and attain the abdominal 

 cavity direct ; some also reach it by means of the lymph stream. 

 Where there are no blood and lymphatic vessels in the intestinal 

 wall, as in insects, the oncospheres attain the body cavity or its 

 organs direct ; in short, they never remain in the intestinal lumen 

 itself, and only rarely as in Hymenolepis murina of the rat do 

 they remain in the intestinal wall. 



When the .infection has been great, and the body is crowded with 

 numerous oncospheres, acute feverish symptoms are induced to which the 

 infected animals usually succumb (" acute cestode tuberculosis ") ; while in 

 other cases the alterations in the organs attacked as the liver in mice, and 

 the brain in sheep may cause death. 



