Slide showing three diagrams illustrating 'metamorphosis of Polygordius.' Slide shows three black and white diagrams illustrating 'metamorphosis of Polygordius.' Title below images reads: 'Fig. 12. Metamorphosis of Polygordius. Upper figure on left, trochophore larva; on right, later stage with worm growing out; lower figure, much more advanced stage, anterior end. (After PARKER and ROULE; much magnified.)' Late 19th to early 20th century