THE SUPPRESSION OF CLEAVAGE IN ASCARIS EGGS BY ULTRACENTRIFUGING

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Abstract
Eggs may undergo typica1 mitotic division of the nucleus without the usual division of the cytoplasm in the centrifuge at 150,000 times gravity. This gives rise to 2 nuclei within the egg, which may in turn form typical mitotic figures and divide at the same time, giving rise to 4 nuclei within the uncleaved egg. After removal from the centrifuge eggs that have undergone one or more divisions of the nucleus without the division of the cytoplasm show a curious peripheral "bubbling," or the extrusion of pseudopodium-like processes in the region of the clear cytoplasmic layer. These pseudo-podia may be cut off from the egg, in which case they undergo rapid ameboid movement. If not detached they are withdrawn into the egg during the redistribution of the stratified materials and subsequent cleavage. This material extruded in the form of pseudopodia, is thought to represent "surface active material," which upon coming in contact with the surface or outside environment of the egg coagulates giving rise to a film or plasma membrane. It is this same material which during normal cleavage concentrates at the periphery of the egg and functions in the formation of the cleavage furrow but which is prevented from acting in the centrifuge. Uncleaved eggs centrifuged at 400,000g for 30 min. are not killed nor is the mitotic figure much distorted and if the stratified materials are redistributed before cleavage takes place they apparently develop normally. No evidence was found which indicates a separation of the ultramicroscopic cytoplasmic components had taken place.

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