Variants of arrangement of sexual glands in Hymenolepididae with three testes: a new approach
Original schemes of all the 19 known arrangement modifications of male and female sexual glands in proglottides of hymenolepidid flatworms with three testes are given. It is suggested to classify the diversity of the gonad topography on the basis of absence or presence of shift of female sexual glands and the male testis in relation to the median axis of the proglottid. Bilateral symmetry in gland arrangement is observed in two modifications ( II and VI ); in 9 modifications, the center of female sexual glands coincides with the median axis. Poral or antiporal shift of female gonads results in the location of the median testis in the median axis. Finally, in modification XII , traces of bilateral gland arrangement are absent: the median testis is shifted anteriorly and female genitals are situated significantly posterior to the posterior testis.