104 BOARD OF AGRICULTURE. 



with an ordinary lens. These tubes commence in fine, rootlet- 

 like branches, with rounded and closed ends, but the small 

 branches constantly unite into larger trunks, which in turn 

 all unite into one main trunk, running along the middle line 

 of the body, and this terminates in an external orifice at the 

 posterior end. The use of this system of tubes is to remove 

 the waste materials from the body. It may therefore take 

 the place both of the kidneys and liver of the higher animals. 

 There is 110 blood circulation and no true blood in these 

 animals. 



Development. 



The fluke is a very prolific creature. Prof. Leuckart esti- 

 mates that the ovaries may at any one time contain 45,000 

 eggs. The number of broods that they produce is not known. 

 The eggs that are discharged pass out of the intestine of the 

 sheep, or other animal in which they live, with the excre- 

 ment. Those that get into water or moist places hatch after 

 several weeks, producing minute conical embryos, which are 

 covered with vibrating cilia or lashes, by means of which 

 they swim freely about in the water. In this state the em- 

 bryo is YJJTJ- of an inch long and -$$ of an inch broad at the 

 larger end. The cilia are T ^ of an inch long. 



In a few days the external skin, with the cilia, is cast off, 

 and after that the embryos are obliged to creep about, instead 

 of swimming. Its farther development has not been traced, 

 but it probably has a history similar to that of other species 

 of flukes of which the entire history is known. Therefore it 

 is supposed that the young embryos, above described, attach 

 themselves to the bodies or enter the tissues of the fresh- 

 water spiral snails, such as Limncea and Physa. In this 

 situation the form probably changes, and they become the so- 

 called " nurses," and then a brood of larvae of another form 

 is developed in their interior, by a process of internal budding. 

 These larvae are provided with a tail and have a form some- 

 what resembling minute tad-poles. In this state they are 

 known as cercarice. They are finally discharged from the 

 body of the " nurses," and escaping from the snails, may 

 again swim actively about in the water, by means of 



