Studies on Centrifuged Frog Eggs

Abstract

The effect of cetitrifuging fertilized eggs of the frog both before cleavage and during the early cleavage stages has been studied by several investigators. Gurwitsch, 1 Hertwig, 2 Wetzel, 3 Morgan, 4 Konopocka, 5 McGlendon, 6 and Jenkinson 7 particularly have reported the redistribution of certain materials and the intense stratification of others along the primary axis of centrifuged frog eggs. They state that the stratification of materials takes place in the order of their relative specific gravity, i. e., a yellow or white centripetal layer, a translucent protoplasmic middle layer and a heavy yolk centrifugal layer containing the black pigment granules. In general, the results of these investigators show that, when the centrifuging has been relatively weak, development is often apparently normal with perhaps a slight abnormal pigmentation and distribution of fat in the head regionl However, if the centrifugal force has been slightly greater, curious monsters often appear. Jenkinson particularly has noted that the myotomes and spinal ganglia are frequently fused together beneath the nerve tube and that the notochord is often absent altogether. Hertwig frequently obtained monstrosities of the spina bifida type. Pasquini and Reverberi 8 have centrifuged frog eggs at the gastrula stage and obtained many curious monsters not unlike some that have appeared in our experiments.

We have recently centrifuged unfertilized frog eggs of Rana aurora for 2 minutes at 40 pounds pressure in the air-driven ultra-centrifuge described by Beams, Weed and Pickles, 9 It has been possible to repeat the stratification of materials in the frog egg as described by the above named investigators. Furthermore, we have produced a complete cleavage or fragmentation of the egg into a light fatty fragment and a heavier yolk and protoplasmic fragment. No effort has been made to determine whether or not such fragments may be fertilized and if fertilized will develop.