The history of the cytoplasmic inclusions of the egg of Ciona intestinalis (L.) during oogenesis and fertilisation

Abstract

Previous accounts of Ascidian eggs are briefly reviewed. Mitochondria, present originally as a few colorless vesicles surrounded by acido-phile aurae, increase greatly in numbers. Except those forming a close-packed peripheral layer, and a few scattered ones, they swell and form yolk droplets. After extrusion of the test-cells from the egg the peripheral mitochondria become granular, forming a deep cup incompletely surrounding the yolk. At fertilization the cup becomes thicker and shallower. The Golgi apparatus, at first diffuse, concentrates to one side of the nucleus. The "yolk nucleus" appears among the Golgi elements at this time and is probably secreted by them. The Golgi bodies again become distributed uniformly in the cytoplasm except in the peripheral layer occupied by the mitochondria. Correlated changes of the cytoplasm from oxyphily to basophily and again to oxyphily, accompany changes of the Golgi apparatus. The yolk nucleus fragments and disappears in the cytoplasm prior to yolk formation. During the latter process lipoid granules of the test-cells disappear, and it is suggested that these and the yolk nuclear material form the basis of yolk.