Fine structure of the uteri in two hymenolepidid tapeworm Skrjabinacanthus diplocoronatus and Urocystis prolifer (Cestoda: Cyclophyllidea) parasitic in shrews that display different fecundity of the strobilae.

Adult specimens of Skrjabinacanthus diplocoronatus and Urocystis prolifer were investigated by light and transmission electron microscopy, and data on the uterine organization in these species are presented. The interrelationships of morphological changes of the uterus and developing eggs on the one hand with fecundities of the strobilae of cyclophyllidean cestodes on the other hand are investigated. The development of the excretory system forming a network of excretory ducts close to the uterus is characteristic of S. diplocoronatus. Numerous excretory ducts are located near the uterus or contact the uterine epithelium and are also found in uterine cords. Accumulation of lipids is observed in the cavity of excretory ducts, in muscular cells, and in the lumen of the uterus as well as in the developing eggs. This species displays the largest fecundity among cestode parasites of the shrew. U. prolifer has one of the lowest fecundities among cestodes from shrews. A small amount of lipids found in cells of gravid proglottids could serve as a supply of nutrients. It seems that some cestodes with great fecundity possess specific paths by which eggs are supplied with nutrients. As a result, diverse modifications of the uterus in Cyclophyllidea are formed.