ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



o) is a much branched organ, lying usually in the 



however the left) half of the body, about a quarter of 



B from front end to hind end. It is continued towards the 



ini(Ml ,K- O i the body as a simple tube-the oviduct. While the ovary 



, iunctional macrogametes, there is present also a great mass 



FIG. 75. 



H.une-rrlls " (highly magnified). A, 1'Ianarian 



B, :nira<-idiiiiii sta^e of Fasciola (Distoma) ; C, 



i ), a I'olvrhaete (Phyllodoce) ; E, 



Amphioxu*. The lii^li'y evolved tubular type of (lame-cell 



i.il name snl, n 



iiiid \vhich may be said to have degenerated,, its cells being 



motional macrogametes but being simply yolk-cells destined 



to provide the xygote with a supply of food material. This degenerate 



Is in the form of innumerable little spherical yolk-glands (y.g), 



'1 in a broad band round the whole margin of the body except 



its extreme front end. In the fresh specimen this band is of a dark 



colour, the yolk being dark greenish, but when the fluke is kept inspirit 



