Microscopic structure of the gravid uterus in the little skate,Raja erinacea

Abstract

The morphology of the uterus in oviparous elasmobranchs has not been systematically examined in any species. The uterus in oviparous sharks and skates houses the eggs during the crucial chemical events that result in the requisite polymerization of the assembled egg capsule materials. Capsule sclerotization involves a quinone tanning mechanism in which catechols are introduced in utero and subsequently oxidized to quinones prior to oviposition. The uterus in Raja erinacea is morphologically specialized for four well-defined functional activities associated with egg capsule formation: regionally distinct structural modifications, both in the uterine wall and the epithelial lining, for active movement of the capsule through the uterine lumen; biosynthesis and secretion of materials into the lumen; vascular facilitation for oxygen transfer to fuel the oxidation process involved in capsule tanning; and intercellular spaces for removal of water from the uterine lumen. The first three activities are qualitatively similar to those operating in viviparous species. The uterus throughout its length has longitudinal folds punctuated by secretory crypts. Proceeding from the anterior to the posterior end of the uterus there is a progressive decrease in the number of cilia and the depth of the lamina propria, and an increase in vascularity and the width of the muscularis. J. Exp. Zool. 282:421–437, 1998. © 1998 Wiley-Liss, Inc.