MATURATION OF OVUM IN ECHINUS ESOULENTUS. 103 



My conception of the meaning of the changes in the ovum 

 does not, however, involve an acceptance of either Stras- 

 bnrger's kinoplasmic or of Boveri's archoplasmic theory. It 

 inclines rather to the view that the same ground substance, 

 under the influence of the chemical changes underlying vital 

 activities, may take on different forms in response to varying 

 physiological needs, and fui'ther, that whereas, during the 

 vegetative period, the main centre of these chemical activities 

 lies in the nucleolus, in the division period that centre is trans- 

 ferred to the centrosome, which is the expression of activities 

 resulting in the vital phenomena of division. 



Fig. 15 i^epresents a later stage. The spindle is not yet 

 complete, but the two asters are situated radially, and the 

 reticular mass, though still showing in some parts a radial 

 distribution from the central plate, is becoming more and 

 more focussed on the centrosomes. The spindle, in most 

 forms, is said to be fully formed before this radial position is 

 assumed, and the whole spindle is said to rotate through 

 90 degrees. A very good example of this is seen in the egg 

 of the mouse, as described by Sobotta (1895). 



In my preparations the spindle, as is the case also in 

 Thalassema (Griffin), is late in being completed, and the asters 

 seem to move independently through the cytoplasm, the fibres 

 arranging themselves round the centre of activity until the 

 definitive position is reached. 



The conditions described for the formation of the polar 

 spindle are not unlike those accompanying the formation of 

 the multipolar spindles described in the pollen and the spore- 

 mother cells in many plants by Farmer, Belajeff, Osterhout, 

 Mottier, Nemec, and Byxbee. According to the description 

 of these authors there is a filar zone round the nucleus, out of 

 which the multipolar figure is spun, the poles of which draw 

 together to form the definitive bipolar spindle. I have seen 

 one or two four-poled first-maturation spindles, but I cannot 

 make out that in the reticular zone there are more than two 

 asters which have any relation to the future spindles, and 

 such four-poled spindles would thus merely indicate the 



VOL. 46, PART 2. NEW SERIES. If 



