The ultrastructure, development and mode of operation of the ventrogenital complex ofCryptocotyle lingua(Creplin) (Digenea: Heterophyidae)

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Abstract
C. lingua, like other Heterophyidae, has no cirrus sac or cirrus. To ensure that cross-fertilization occurs, an elaborate ventrogenital complex has developed to enable 2 individuals to remain firmly attached while mutual exchange of sperms takes place. The ventrogenital complex consists of a ventral invagination and the ventrogenital sac, containing a protrusible gonotyl in the apex of which is embedded the modified ventral sucker. An anterior pocket opens into the ventrogenital sac anteriorly, and the male and female genital pores posteriorly, dorsal to the root of the gonotyl. During copulation 2 individuals face in opposite directions, their ventral surfaces being closely applied and the gonotyl of each lying opposite the anterior pocket of the other. The arrangement of muscles suggests the mode of operation, namely, the gonotyl (and ventral sucker) of one enters the anterior pocket of the other, simultaneously, so that the 2 individuals are pulled closely together and held firmly. The protrusion of the gonotyl brings the genital pores of both individuals into close proximity, the male pore of one being opposite the female pore of the other as they face in opposite directions. An arrangement of grooves in the adjacent surfaces of the gonotyls ensures a mutual flow of sperms from the male pore of one to the female pore of the other, the flow being initiated by contraction of the circular muscles around the ductus ejaculatorius in each. The ventrogenital complex develops in the encysted metacercaria in the fish 2nd intermediate host. At 38 days old, the stage infective to the bird, all essential parts of the ventrogenital complex are present.

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