Structural Aspects of Ovulation in the Lamprey, Petromyzon marinus

• Published in: Biology of reproduction Vol. 22; no. 4; pp. 897 - 912
• Main Authors: Yorke, M A, McMillan, D B
• Format: Journal Article
• Language: English
• Published: United States Society for the Study of Reproduction 01.05.1980
• Subjects: Animals; Female; Fishes - physiology; Lampreys - anatomy & histology; Lampreys - physiology; Microscopy, Electron; Microscopy, Electron, Scanning; Oocytes - growth & development; Oocytes - ultrastructure; Ovary - physiology; Ovary - ultrastructure; Ovulation; Ovum - growth & development
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod22.4.897

The mechanism of ovulation in vertebrates is poorly understood but most theories suggest fluid pressure or muscular contraction as the force expelling the egg from the follicle. The simple follicle of the lamprey, Petromyzon marinus , was used in this study for the analysis of its various components during ovulation. Three distinct layers of cells surround the oocyte. The innermost is the follicular layer. The apical follicular cells secrete the fluid of ovulation prior to rupture, thereby elevating themselves from the surface of the oocyte. The adhesive cells are a specialized group of follicular cells which form a cup around the basal two-thirds of the oocyte. They undergo autolysis and the resulting debris forms a lubricating fluid layer between the oocyte and its investing layers. Rupture of the follicle results from enzymatic degradation of an area of the follicular wall bordering on the coelom. Extrusion of the egg is accomplished by a decrease in the enclosed volume of the follicle brought about by changes in the shape of the follicular cells. These changes begin at the apical end of the follicle, opposite the point of rupture, and progress basally. It is this change in the shape of the follicular cells which provides the force which expels the egg from the follicle.