(_f_) _Cercariæ_ (Figs. 153—155).—These organisms are similar to the adult parasites into which they later develop. The body is flat, more or less oval, and provided with a tail inserted at the posterior extremity. The oral sucker and acetabulum are present as in the adult, but the intestinal tract is very simple; on the sides of the body are seen two large glands, but the complicated genital organs of the adult are not visible. The cercaria leaves the redia through the birth opening, remains in the snail for a longer or shorter time, or passes out of the body of the snail and swims about in the water. After a time it attaches itself to a blade of grass (Fig. 154) or some other object, and forms a cyst around itself with material from the large glands, at the same time losing its tail. It now remains quiet until swallowed by some animal. Then, upon arriving in the stomach—of a steer, for instance—the cyst is destroyed, and the young parasite wanders through the gall-ducts or, as some believe, through the portal veins to the liver, where it develops into the adult hermaphrodite. [Illustration: $1] From the above we see that this parasite runs through three generations, namely: (1.) Ovum, miracidium, and sporocyst ... first generation. (2.) Redia ... second generation. (3.) Cercaria and adult ... third generation. During this curious development, which lasts about ten to twelve weeks, there is a constant potential increase in the number of individuals, for each sporocyst may give rise to several (five to eight) rediæ, each redia to a larger number (twelve to twenty) cercariæ, and each adult to an enormous number (37,000 to 45,000) of eggs. This unusual fertility of the parasite is necessary because of the complicated life history and the comparatively small chance any one egg has of completing the entire cycle. =Hosts.= An interesting and, from an agricultural standpoint, an important matter connected with this fluke is that it is found in a large number (about twenty-five) of domesticated and wild animals, and this fact probably explains to some degree the wide geographical distribution of the parasite. [Illustration: $1] =Symptoms.= The symptomatology of this disease may clinically be divided into three well-marked periods: