510 



THEOPHILUS S. PAINTER 



trotus lividus and to show how the interpretation of the facts 

 here throws light on spiral asters; a phase in the history of the 

 centrosome which has been a dark chapter since Mark, in 1881, 

 first described, and figures ' spiral asters' for Limax campestris. 



The monaster eggs, in which the phenomenon has been ob- 

 served, were produced by shaking violently a few minutes after 

 the fertilization membrane had been formed. Series were pre- 

 served at frequent intervals (from 3 to 15 minutes depending 



on the stage) either in Boveri's picro-acetic mixture or in subli- 

 mate acetic. Sections were cut at 7 m- The stains used were 

 Heidenhain's haematoxylin followed by Lichtgriin. 



As previously mentioned the living egg which showed the spiral 

 aster had been treated with phenyl urethane and then washed 

 in pure sea water. When first observed, the majority of the 

 eggs (treated in the same way) were in the 2- and 4-cell stages. 

 This one egg, however, was undi^'ided and judging from the 

 excentric position of the spindle, had passed partially through a 

 monaster cycle. (The treatment of the eggs with this narcotic 

 frequently produces monasters.) Two general centers of radia- 

 tions were seen, with a very faint spindle between them. The 

 rays were very much bent, as may be seen from figure A, and the 

 spindle itself lay at an angle to the pigment band.^ As the egg 



' The eggs of the female upon which this experiment was made showed the 

 pigment ring very clearly. This aUowcd me to mark the position of the spindle. 



