348 Veterinary Medicine. 



2. The ciliated embryo swimming free in fresh water. 



3. Brood capsule in the body (usually chest) of a mollusc. 



4. Redia in parenchymatous organ (usually liver) of a mollusc. 

 In winter one or more crops of daughter redise in same. 



5. Cercaria swimming free in fresh water. 



6. Cercaria encysted in glutinous matter on aquatic plants. 



7. Young fluke set free in stomach and duodenum and enter- 

 ing the biliary ducts, of a mammal. 



The ova may number 30,000 to 40,000 from a single fluke, 

 (Thomas, Neumann). When set free in the bile ducts, bowels, 

 or outside in water at 23° to 36° C. they undergo segmentation 

 and develop an embryo which may escape in 3 to 6 weeks by 

 pressing open the operculum. 



The embryo 130 /x by 27 /*, is a flattened organism, like a micro- 

 scopic distoma, being broad in front and narrowed behind, the 

 outline being oval. From the middle of its cephalic or thick end 

 projects a .sharp, protractile, conical papilla by the aid of which 

 it bores its way into its victim mollusc. In the anterior part of 

 the body is a dark crucial object (digestive apparatus, Ivcuckart), 

 the interior of the body contains granular cells, and its cutaneous 

 layer consists of polygonal cells bearing an abundance of cilia, by 

 the aid of which the embryo swims in water with great rapidity. 

 If it fails to find a molluscous host it usually dies in eight hours, 

 though in a slightly alkaline fluid it may survive for three days 

 (Thomas). 



The embryo coming in contact with a soft skinned mollusc, in- 

 stantly attacks it, projecting its conical borer into its skin, and 

 rotating its body with great rapidity, alternately elongating and 

 shortening it, until it has completely disappeared in its substance 

 when it proceeds to encyst itself by preference in the pulmonary 

 space, but also at tinies in the general body cavity or in a solid 

 organ such as the foot, in which last, however, it usually perishes 

 for lack of room to grow. 



The mollusc which forms the usual host is the Limncea Trunca- 

 tula, a small, .soft, gray gasteropod with a shining shell ^ inch 

 in length and having 5 turns in the spiral. This is found very 

 abundantly in most parts of the world, up to an altitude of iioo 

 to 1200 metres. It is absent in salt marshes, and has not been 

 demonstrated in the Shetlands, Australia nor America, although 



