314 EDWIN G. CONKLIN 



2. General aims and results of this work 



It was with a view to determine more exactly whether there 

 is a 'ground substance' which remains unmoved in centrifuged 

 eggs, or whether the morphogenetic substances of the egg are 

 moved with the other substances and later resume their nor- 

 mal positions that the following work was undertaken. The 

 eggs upon which these experiments were performed were those 

 of the marine gasteropod, Ci'epidula plana. This object was 

 chosen not only because of my familiarity with its normal de- 

 velopment but also because the yolk in this egg is so abundant 

 that any change in its position involves marked changes in the 

 positions of nuclei and cytoplasm, which are presumably parts 

 of the 'ground substance.' 



If the eggs of this gasteropod are subjected, after fertilization 

 and before the first cleavage, to centrifugal force of approximately 

 600 times gravity, the yolk is thrown to the centrifugal pole, 

 where it occupies about three-quarters of the volume of the 

 whole egg; the middle zone, consisting of nucleus and clear cyto- 

 plasm, comprises a little less than one-quarter, and the oil zone 

 constitutes about one sixty-fourth of the volume of the entire 

 egg, the relative volumes of the three zones being 49: 14: 1. In 

 normal eggs of this stage the nucleus, centrosphere and most 

 of the cytoplasm lie near the animal pole, but in centrifuged 

 eggs these formative substances may be displaced far from this 

 position, the yolk, for example, being thrown to the animal pole 

 and the protoplasm to the vegetal one, or these displacements 

 may take place in any other axis. Nevertheless such eggs fre- 

 quently develop normally, showing that the polarity and pat- 

 tern of organization of the egg have not been permanently 

 changed by this dislocation of the formative materials. It 

 seems necessary to conclude that there is some material substance, 

 or relation of parts, in these eggs which persists with relatively 

 little change, in spite of the dislocations caused by centrifuging, 

 but if there is a 'ground substance' here which is not moved by 

 centrifugal force it must be a relatively small part of the gen- 

 eral protoplasm of the egg. 



