84 DISEASES OF THE DIGESTIVE APPARATUS 



Tape-worm. 



Natural History. — The cestodes are flat tape-like worms without 

 mouth or intestines. They grow from one parent or head scolex and 

 adhere together, in a long ribbon-like colony. The head is furnished with 

 sucking cups and hooks, by which means it adheres to the mucous mem- 

 branes of the intestines. The parasite is narrow at the neck, gradually 

 widening and at its termination it consists of a number of matured seg- 

 ments that separate from the parent parasite, when they are fully de- 

 veloped, and are carried out among the faeces. Each segment is complete 

 in itself, having both male and female genital organs. This order are 

 hermaphrodites and are peculiar from the fact that they produce the 

 germs of the new nursing mothers, of the shape of eggs, while the nurse 

 remains sexless. The ripe segments (proglottides) are soon detached and 

 pass either into manure, or in water, plants or grass. The proglottides 

 break up and the eggs scatter in all directions. The eggs are covered 

 with a hard, tough shell, inside of which is a six-hooked embryo. If the 

 egg is taken into the stomach, the acid gastric juice dissolves the shell; 

 the embryo is liberated, and immediately fastens the hooks into the mucous 

 membrane of the intestine and from there penetrates into the connective 

 tissue of some of the adjacent organs, where it forms a sac-like cyst. 

 These cysts contain fluid, and are termed bladder worms, when empty 

 and cysticercus or cysticercoids when they contain fluid. In each of these 

 bladders we find the individual taenia head furnished with hooks and the 

 sucking caps. In some forms of the taenia these bladders divide and sul)- 

 divide into numerous daughter-cysts or breeding buds, all of which pro- 

 duce the little heads of the taenia. This is frequently seen in the echino- 

 coccus, where enormous masses are found. If any animal, or proper 

 secondary host, gets one of these ripe bladder worms into the stomach the 

 gastric juice dissolves its covering and it finds its way to the duodenum, 

 where it fastens itself by means of its hooks and sucking apparatus and 

 instantly becomes a breeding parasite. 



The anatomical structure of the cestodes is very simple. The body 

 parenchyma is divided into two layers, an external and an inner covering. 

 In the latter, we find the sexual organs. The external layer is chiefly 

 muscular, and contains also a mass of calcareous nodules that replace 

 the defective bony structure of the cestodes. The surface of the head 

 is covered with a skin or cuticle, from which the hooks originate. A 

 digestive system and blood vessels are absent, but in the inner layer we 

 find a system of very much branched water vascular sj^stem, which is 

 connected with two elongated canals, united at each joint by a cross 

 system of similar canals, which is said to serve as an excretory apparatus. 



