It has been compared with the canal of Laurer of Trematodes (the vitello-intestinal duct of the ectoparasitic flukes), but if we take the more primitive Cestodes, and especially Aniphilina, into consideration we find that they possess, in addition to the uterus, an anterior vagina (usually present in Cestodes) and a posterior one.
In B it is also joined by a paired vagina k, k, and by the " vitello-intestinal duct " (La.urer's canal, f).
127 9, these problems were taken up by three almost contemporaneous writers on optics, two of whom, Roger Bacon and John Peckham, were Englishmen, and Vitello or Witelo, a Pole.
Archbishop Peckham, or Pisanus, in his Perspectiva Communis (1279), and Vitello, in his Optics (1270), also attempted the solution of Aristotle's problem, but unsuccessfully.
In B it is also joined by a paired vagina (kk) and by the "vitello-intestinal duct" (Laurer's canal), f.
(c) Shell-glands; (d) ootype; (e) uterus; (g) median-vitello-duct; (i, i) intestine.
A, Dorsal view showing the nervous system and digestive system; a, mouth; b, pharynx; c, d, e, gut; E, post-genital union of two limbs of gut; f, excretory pore; g, vaginal pore; h, j, k, brain and nerves; 1, dorsal nerves; m, ventral nerves; n, adoral sucker; o, posterior sucker; p, hooks on posterior sucker; r, vitello-intestinal duct.