WORMS. 



57 



pie, while others are far more complex, but most of them have a shape 

 which renders their common name appropriate. They are long and flat 

 like a ribbon, and unlike most worms they are without a digestive sys- 

 tem. Their parasitic life has caused a degeneration, and at last a disap- 

 pearance, of all of the alimentary canal ; but the lack of this is of no great 

 importance, for they obtain their food from the intestine of their host 

 largely in a digested condition. They do not need a mouth, because the 

 whole surface of the body possesses absorptive powers. 



Several very distinct groups of tape-worms exist, differing not only in 

 their general appearance, but in their life history ; but of these we need 

 concern ourselves only with those which inhabit mankind, merely saying 

 that almost every species of the higher animals, and many of the lower 

 forms, have their peculiar species. For most of our knowledge of these, as 

 well as of almost every branch of exact zoological knowledge, we are 

 obliged to go to those indefatigable students, the Germans, notwithstanding 

 the fact that America is as fully provided with these 

 pests as is the Old World. 



Most important of all are the species of Tcenia, of 

 which three species are comparatively common in man, 

 Tcenia solium being the most abundant and the best 

 known. It has a small head, about as large as the head 

 of a pin, but this has no mouth and but the merest 

 apology for a brain. It in reality serves as an anchor 

 for the rest of the animal, and for this purpose it is well 

 adapted. This head burrows beneath the lining mem- 

 branes of the intestine, and the hold thus obtained is 

 further strengthened by the four suckers on the sides 

 and a crown of hooks on the top. From this head 

 proceeds a long, slender, ribbon-like neck, which at first 

 is even narrower than the head, but it gradually widens 

 out until the body reaches a breadth of a quarter of an 

 inch. Behind the head, the whole body is broken up 

 into a series of joints or ' proglottids,' which increase in 

 length with their distance from the head. These joints 

 arise just behind the head, and as newer ones are 

 formed the older ones are pushed farther back. With 

 this increase in distance comes one in size, and grad- 

 ually each joint forms eggs, until at last, when fully "ripe," it maybe 

 regarded merely as a bag of eggs. When the proper time comes, each 

 joint drops off from the chain and is discharged from the body with the 

 egesta. After thus escaping, the eggs contained in the joint pursue a part 



Fig 



— Diagram of I In- 

 different parts of a tape- 

 worm, showing thehead, 

 neck, and the character 



pf the segments in dif- 

 ferent regions of the 

 body. The entire ani- 

 mal could not be shown 

 on account of its great 

 length. Above is the 

 head, enlarged. 



