STUDIES WITH THE CENTRIFUGE 43 



A section of an egg centrifuged forty-five minutes after ferti- 

 lization, killed immediately in picro-sulphuric and stained with 

 Delafield's haematoxylin and orange G is shown in fig. 11). The 

 spindle lies in the purple zone close under the cap and parallel to 

 the stratification. Of forty-two spindles recorded in this position, 

 six were equatorial plates, ten were in metaphase and twenty- 

 six in anaphase. A great many more eggs were studied in an 

 effort to find a spindle lying perpendicular to the layers. No evi- 

 dence of such a condition was found, which bears out the evidence 

 already recorded in the living eggs, where the cleavage is always 

 perpendicular to the layers. 



The spindle does not occupy its normal position in center of 

 the egg but lies toward the top in the protoplasmic band just 

 under the cap. The first question is in regard to orientation. 

 The constant relation w^hich Morgan described between the micro- 

 pyle and micromeres showed beyond doubt that the unfertilized 

 eggs do not orient themselves in the machine. It was possible, 

 however, that the case might be different after the spindle had 

 formed. As a means of testing the point, I centrifuged eggs in 

 the late 2-cell stage, and found that the stratification bore no 

 definite relation to the first cleavage plane; that is, the layers 

 were in some eggs perpendicular to the cleavage plane, in others 

 parallel or oblique. Some of the eggs were killed at once and 

 found to contain spindles. The eggs, therefore, do not orient 

 themselves in the spindle stages of the 2-cell egg and I see no 

 reason to suppose that they do so immediately before first cleav- 

 age. 



Since the eggs do not orient themselves in the machine and yet 

 the spindles always maintain a definite relation to the centrifugal 

 layers, it follows that in many eggs the spindle will not chance to 

 be perpendicular to the line of force and in such cases something 

 more than a pushing to one side of the karyokinetic figure occurs. 

 The most striking evidence of this in the sea urchin occurs in the 

 spindle stages of the 2-cell stage described above. When the 

 stratification is perpendicular to the cleavage, the spindles are 

 parallel to the layers and to the cleavage plane and consequently 

 to each other. If the stratification is parallel to the cleavage plane 



