54 BOARD OP AGRICULTURE. 



from the enclosing proglottid after the latter has been dis- 

 charged from the animal that nourishes the parent tape-worm. 

 The eggs usually escape by the bursting of the integument of 

 the proglottid, owing to their increase in size, as the embryos 

 develop within them. While attached to the tape-worm the 

 successive joints are connected -together by longitudinal tubes 

 or ducts that pass through the entire length of the worm-, gen- 

 erally one near each edge of the joints. These are connected 

 together by transverse tubes in each end of the successive 

 joints (Figure 54). 



The reproductive organs occupy variously branched and 

 ramified cavities in the interior of the joints, communicating 

 by ducts with the external male and female organs, which are 

 placed side by side, either on the edge of each joint, as in 

 Tcenia, or in the middle of one side, as in BotTiriocephalus. 

 The remainder of the joint is composed of a firm, more or 

 less solid tissue. 



All the species of this order undergo remarkable metamor- 

 phoses ; the larva living in one animal must be swallowed by 

 another before it can become mature. 



II. TREMATODES. (Flukes). 



This order includes a great number of more or less flattened 

 worms, of which the " fluke," frequently found in the liver of 

 sheep, causing the " rot," is an example (Figure 73). 



The body is generally broad and more or less oval, some- 

 times elongated, but never divided into distinct joints. On 

 the lower side there is usually one or two prominent suckers, 

 and sometimes several. There is a small mouth on the lower 

 side, usually near one end, but no head. The mouth com- 

 municates with a small, dilated oasophagus or stomach, and 

 this with a more or less branched and subdivided, sometimes 

 arborescent, intestine, the branches ending in closed tubes or 

 blind-sacs. Another system of branched and often much sub- 

 divided tubes arises in the more or less solid tissues of the 

 body. These tubes are at first small, like rootlets, but grad- 

 ually uniting into larger and larger branches, finally empty 

 their contents into one or two main trunks, which open ex- 

 ternally by one, or sometimes two orifices, near the posterior 

 end of the body. This is called the water-vascular system, 



