[In the germ ball or morula appears an invagination, giving rise to the cup-shaped gastrula stage. This elongates and forms the REDIA (fig. 131, _c_). [In the interior of the redia cells are budded off and develop into gastrulæ, as in the case of the sporocyst. These become a fresh generation of rediæ or give rise to the third stage (CERCARIA).] [Illustration: FIG. 132.--Young redia of _Fasciola hepatica_, with pharynx and intestine, with a circular ridge anteriorly and a pair of processes posteriorly and masses of cells (germ balls) in the interior. Magnified. (From Leuckart.)] [Illustration: FIG. 133.--Older redia of _Distoma echinatum_, with rudimentary intestine _i._; cercariæ, _c._; germ balls, _b._; and birth pore, _g._ Magnified.] (2) The SPOROCYSTS, on the contrary, which are produced direct from the miracidia, are very simple, as all the organs of the latter disappear, even to the muscles and excretory organs, during or after penetration into the intermediate host, whereas the budded and still budding cells of the wall of the (primary) body cavity continue to develop rapidly and form germ balls. The sporocysts when fully developed have the appearance of tubes or fusiform bodies with rounded edge; they are frequently of a yellow colour. Their length rarely exceeds a few millimetres; in some species their size increases exceedingly through proliferation, and they then occupy a large portion of the body of the intermediate host. (3) The REDIÆ (figs. 132, 133), on the other hand, are more cylindrical and always have a simple intestine of varying length, provided with a pharynx; they likewise possess, situated near the circular ridge, a “birth pore” which serves for the exit of the cercariæ originating within them. [Illustration: FIG. 134.--Cercaria of _Fasciola hepatica_; the cutaneous glands at the side of the anterior body. Magnified. (After Leuckart.)] [Illustration: FIG. 135.--Encysted cercaria of _Fasciola hepatica_. Magnified. (After Leuckart.)]