524 THE COMMON TAPE-WORM. 



alimentary canal passes along each side of the animal, 

 sending a cross canal over the bottom of each joint, 

 which connects the two lateral canals together. The 

 internal structure of the joints is partly cellular and 

 partly vascular : the substance itself is white, and in 

 its texture somewhat resembles the coagulated lymph 

 of the human blood. 



The food of the Taeniae, requiring probably very 

 little change before it becomes a part of their body, 

 is taken in at the mouth, and, being thrown into the 

 alimentary canal, is made to visit, in a general way, 

 every part. The central structure of the vessels 

 placed in each joint seems calculated to absorb the 

 fluid from the alimentary canal, for the purpose of 

 sustaining and repairing the immediately adjacent 

 parts : but there is in their bodies much cellular 

 substance, into which no vessels enter. Such parts 

 of the bodies of these animals are possibly nourished 

 by transudation of the alimentary fluid into their 

 cells ; or this may be effected by the capillary at- 

 traction of their fibres. As they have no excretory 

 ducts, the decayed parts of their bodies are most 

 probably dissolved into a fluid which transudes 

 through the skin like perspiration, and with this 

 view the skin is extremely porous. 



The length of the present Taenia is generally from 

 three to thirty feet ; but it has been known to reach 

 sixty feet, and to be composed of several hundred 

 joints. 



When these worms produce a diseased state of 

 body, those remedies (as drastic purges) are sup- 

 posed to be the most effectual that operate partly 

 4 



