280 DARWINISM AND THE PROBLEMS OF LIFE 



pig's muscles. Fluid passes into the capsule from the 

 surrounding tissue, so that it may swell to the size of 

 a pea. The animal itself remains at the globule-stage, 

 and grows very little inside it. It forms the head of a 

 future tape-worm, and remains at this stage in the 

 muscles of the pig. At this period it is known as 

 a scolex or measle-worm. 



If the infected flesh of the pig is eaten by a human 

 being, the measle- worms are set free, and the small tape- 

 worm head makes its way into the intestine, and attaches 

 itself to the wall. The vesicle hangs on to it for some 

 time, but is at last cast off, and the head begins to form 

 the segments until the animal has reached its full size 

 of more than three yards. 



The development of the 7i-8|- yards long Tania 

 saginata is similar to this. But in this case the eggs 

 must be taken into the stomach of a cow, if they are 

 to become scolices ; the pig digests them. Hence it 

 is that in this case the parts of the worm have 

 developed the power of motion, as the cow does not 

 eat faeces like the pig ; but it can very well happen 

 for the cow to swallow a part of a tsenia clinging to 

 a blade of grass, or grass covered with its eggs. But 

 there is a second difference of more importance to 

 human beings. While the eggs of Tcsnia saginata 

 may safely be eaten by human beings, as they cannot 

 develop in their alimentary canal, it is otherwise with 

 Tcenia solium. In the latter case infection is possible, 

 as the eggs produce larvae in the human intestines as 

 well, and these pass into the muscles, and enclose 

 themselves in capsules as large as peas. If they 



