Some studies on the surface layer in the living egg cell

Abstract

The results recorded here were obtained through the use of Barber's mechanical pipette holder somewhat modified for microdissection purposes. The cells experimented upon were the egg cells of the starfish and of the sea urchin. The eggs, which are somewhat over 1/10 of a millimeter in diameter, were placed in a drop of sea water hanging from the roof of a moist chamber. The microscopically fine tips of the glass dissecting needles projected into the moist chamber and up into the hanging drop. By manipulation of the screws of the mechanical pipette holder the cells in the hanging drop could be dissected with considerable accuracy and an estimate ascertained of their physical consistency. Detailed accounts of Barber's apparatus and its application to microdissection have already been published. The egg cells studied consist of a decidedly fluid interior surrounded by a more solid surface layer of appreciable thickness. This surface layer is most solid on its external surface. Internally its consistency seems to merge insensibly into that of the fluid interior. The inner surface of this layer adheres to the touch. This is demonstrated by introducing a microdissection needle into an egg and pushing the needle through until its tip comes into contact with the inner boundary of the surface layer on the side of the egg opposite the puncture. On withdrawing the needle the layer adheres to the needle tip and strands are drawn into the interior of the egg. If the surface layer be torn while the egg is kept under compression the fluid interior will bulge out through the tear. The cytoplasm, on coming into contact with the surrounding water, tends to establish a definite surface film which prevents the cytoplasm from mixing with the water.