Oviduct, Egg, and Egg Sac Structures in the Siberian Salamander, <i>Salamandrella keyserlingii</i> (Caudata, Hynobiidae): a Histological and Histochemical Study

Abstract

Unraveling morphological and chemical features of the eggs’ jelly layers and other clutch elements, formed by the oviduct of a female, is necessary for the understanding of reproductive adaptation in amphibians. Our study is the first microstructural and histochemical descriptions about the complexity of oviduct, ovisac, jelly layer of the ovum, and egg sac in hynobiid salamanders. We examined female Salamandrella keyserlingii in preovulatory (gravid) and ovulatory (spent) conditions using anatomical, histological, and histochemical methods. Each ovum was covered with two jelly layers. All ova from one oviduct fell into one egg sac. Inner space of the oviduct, in which ova were passed through, was filled with jelly-like substances designated as «intermediate fluids». We named the membrane-like outer layer of the egg sac as «theca». Jelly layers surrounding the ovum were formed by the oviducal tubular glands of the pars recta and pars convoluta of the oviduct, consisting of acidic and neutral glycoproteins. In the ovisac (i.e., homologous uterus), there were three glandular regions and one aglandular dilatable ovisac. Of the ovisac, glands A, B, and C secreted acidic and neutral glycoproteins for the intermediate fluids, neutral glycoproteins for the theca, and mucus-like materials with a neutral glycoprotein nature, respectively. We suggest that these mucus-like materials are essential to attaching the adhesive tips of the egg sacs to some substrates during oviposition.