360 INSECTS INFESTING DOMESTIC ANIMALS. 



from this time until it is hatched is unknown, Ijut moisture in 

 some form is probabh^ necessary to its development. It is 

 next found in the body of some mollusk, as the snail, or some 

 aquatic insect, where its form is so different from that of its 

 after-life that it was long considered as appertaining to an 

 entirely different group of animals. From these, in some way 

 not yet ascertained, it passes into the sheep. It ]>robably 

 escapes from the mollusk or insect to herbage in moist places, 

 or water, and is taken into the stomach of the sheep with its 

 food or drink, and passes through the lacteals, and makes its 

 way into the ducts of the liver. 



' As sheep do not feed on mollusks as the water-birds do, it 

 is ditlicult to imagine how the cercaria, if it becomes encysted 

 in tlic body of the mollusk, makes its way into the stomach of 

 the sheep. It is possible this may be explained in one of two 

 ways. First, as has been stated above, the cercaria is for a 

 time a free swimmer, and hence may be taken into the 

 stomach when drinking, or attached to herbage in damp 

 places. Second, it has been ascertained by Van Beneden that 

 some species of this group pass to the mature state directly 

 from the redia stage without undergoing the intermediate or 

 cercaria stage ; as these are free they may be taken into the 

 stomach in water or on damp herbage. 



' As before stated, these internal parasites are supposed to be 

 the cause of rot in sheep, though many persons are inclined 

 to believe they are a consequence rather than a cause of 

 disease. Hut all appear to agree that this disease is connected 

 with the condition of the soil, or the state of weather, moisture 

 being the element most likely to produce it. This corre- 

 sponds exactly with the theory of its life history which I have 

 presented, and indicates the best means of preventing it, to 

 wit : Give them well-drained, o\n'\\. airy pastures, and proper 

 protection in damp and rainy seasons. It is more probable 

 the condition of sheep is often attributed to this disease, wlien 

 it is due to other causes.' " 



