44 GEORGINA B. SPOONER 



the spindles are likewise parallel to the layers and the first cleav- 

 age, but they are not always parallel to each other, which is an 

 unusual condition. However, the eggs in which the stratifica- 

 tion is oblique to the cleavage are yet more unusual for the spin- 

 dles are always parallel to the layers and not to the cleavage 

 plane. They may also be perpendicular to each other. The 

 results mean certainly that the spindle is not only shifted to one 

 side but is in many cases swung through a considerable arc into 

 its new position. 



The second cleavage in centrifuged eggs where the layers are 

 oblique to the first cleavage plane offered an opportunity of test- 

 ing the influence of stratification upon the direction of cleavage. 

 A number of eggs were observed. In every case the second cleav- 

 age was perpendicular to the first cleavage. There is only one 

 meridian through which a plane can pass which will be perpen- 

 dicular to the oblique layers as well as to the first cleavage. In 

 some cases the second cleavage cut through that meridian. When 

 this was not the case a shifting of the layers gradually took place, 

 so that when the second cleavage cut through, the layers had 

 become parallel to the first cleavage plane. The second cleavage 

 plane was then perpendicular to the layers as well as to the first 

 cleavage. 



To find that the cleavage spindles can be moved, although 

 the moving be nothing more than a shifting of the whole figure 

 to one side, bears on our conception of the structure of the kary- 

 okinetic figure. That the substances of the egg are subject to a 

 greater condition of tension or ''rigidity" during karyokinesis 

 than in the resting stages must be true for the materials of the 

 egg are very much harder to separate at that time. ^Nevertheless 

 the spindles contained in eggs, killed immediately after centri- 

 fuging, are to all appearance uninjured, despite the fact that they 

 have been at least pushed from their normal position in the center 

 of the egg and often rotated into a position parallel to the layers. 

 The eggs are spherical after centrifuging as they are normally 

 and this probably accounts for the absence of any distortion in 

 the general shape of the spindle such as has been described in 

 Cyclops. 



