293J XORTIl AMEKICAX POLYSTOMIDAE—STUXKARD 13 



not homologous witli Laurer's canal, coiu-huled that it had arisen sui 

 generis. 



On the basis of these differences in the female genital duets he 

 divided the Mouogenca into two suborders : Monopisthocotylea and Poly- 

 opisthoeotylea. The former is characterized by the absence of tlie gonito- 

 intpstinal canal, the presence of a "true vagina" and a single pos- 

 terior organ of attachment; the latter bj- the presence of the genito- 

 intestinal canal, "ductus vaginalis," many posterior adhesive organs, 

 and the absence of a "true vagina." In the Monopisthocotylea 

 he included the families Tristomidae, jMonocotylidae, Udonellidae 

 and Gyrodactylidac ; and in the Polyopisthocotylea the families 

 Polystomidae, ]\Iicrocotylidae and Octoeotylidae. He pointed out that 

 by tlie removal of the genus Sphyranura, the Oligocotjdea, the first of 

 Jlontieelli's tribes agrees entirely with his suborder llonopisthocotylea. 

 In the second of Mouticelli's tribes, however, the Diclidophorinae, to- 

 gether with the genera Dactylocotyle and Hexacotyle, should be re- 

 moved from the Octoeotylidae and placed with the Microcotylidae, since 

 the}- more nearly agree with the latter forms in internal structure. 



The next year Odhner (1913) reaffirmed his idea of the homologj' 

 of the vagina of the cestodes and Laurer's canal of the distomes, 

 but explained therewith that his denial of the homology of the 

 genito-intestinal canal and Laurer's canal had been based on an error of 

 Cerfontaine in describing an unpaired vagina as present in the genus Dac- 

 tylocotyle. On examination of this genus ho had found that a "true 

 vagina" was absent, and concluded that tlie "true vagina" of the Mono- 

 pisthocotylea which lie had homologized with Laurer's canal was never 

 j)resent together with the genito-intestinal canal. From this he decided 

 tliat tlie "true vagina" was homologous with the genito-intestinal canal 

 ami therefoi-e with Laurer's canal. Now maintaining the homology of 

 the "true vagina'' and the genito-intestinal canal he is i;i my opinion 

 obliged to dismiss the presence or absence of the genito-intestinal canal 

 as a basis of difference between his suborders, and explain why in one 

 group this canal opens to the exterior on the ventral side of the body 

 and in the other opens into the intestine. His homology of the "true 

 vagina" and the genito-intestinal canal is a most serious error since it 

 would invalidate tlic distinguishing feature which separates the two 

 suborders. 



I propose to sliow that the organ which functions as a vagina is 

 liomologous in all tlie monogenctic trcmatodes, and that there can be no 

 division of the group on the basis of difl^'erences suggested by Odliner. 

 In fact, the work of Odhner is based on an incorrect assumption and 

 false homologies. Starting with the assumption that Laurer's canal is 

 homologous to the vagina of the cestodes, he has missed the truth in his 



