Fig. 3

Alternative interpretations of the antero-posterior (AP) polarity of the strobila. In tapeworms, the AP polarity of the scolex (red) has been definitively fixed by the gene expression studies of Koziol et al. [8] in Echinococcus multilocularis and Hymenolepis microstoma. However, the verdict is still open on the question of the polarity of the proglottids. These are generally interpreted as being polarized in concordance with the scolex (a), but the localization of the body region from which the proglottids proliferate as well as the relative position of testes and ovaries within each proglottid suggest the alternative interpretation (b)