490 THOMAS n. BIJYCK. 



division proceeds as in normal fertilisation. If more than 

 two asters are formed from the nuclear area, multipolar figures 

 form, and irregular cleavage results. If there is only a single 

 radiation which does not resolve itself into a bipolar figure, 

 the egg never properly segments, but there are regularly 

 alternating phases of nuclear transformation. 



Analysing the meaning of the phenomena, Wilson says, " Wo 

 may therefore state that the first general effect of the stimulus, 

 whether the magnesium solution or the spermatozoon, is to 

 arouse an activity of the cytoplasm, one result of which is the 

 establishment of a centripetal movement of the hyaloplasm 

 towards one or more points at which the hyaloplasm accumu- 

 lates." The rays in this view are the expression, in part at 

 any rate, of centripetal currents, and the substance flowing 

 in, is the hyaloplasm or interalveolar substance. The hyalo- 

 plasm spheres at the centres of the asters are local accumula- 

 tions of this hyaloplasm. In fixed material, studied in 

 sections, the radiations are fibrillar in appearance, and as 

 they stain much more deeply than the general network 

 the hyaloplasm in the rays must probably have undergone 

 some physical or chemical change. The centrosome is a 

 well-defined body of considerable size and of spongy con- 

 sistence, composed of intensely staining granules, which often 

 give the centrosome the appearance of a minute nucleus 

 containing a chromatin reticulum. The hyaloplasm spheres 

 in the living egg corresjjond to the centrosome, the clear area 

 round it, and the innermost darkly staining radiated zone of 

 the aster taken together. 



Thus Wilson lias proved that structures which cannot be 

 distinguished morphologically from 'Hrue centrosomes" 

 appear in the cytoplasm do novo; and further, that they 

 divide to form the apices of bipolar figures, even in enucleated 

 fragments. 



In a recent paper Moves (1902), using Eoveri's nomen- 

 clature, expresses the view that the centrosome is only the 

 mantle of the centriole, and is oidy present in rapidly-dividing 

 cells like the blastomeres. The " Doppelkcirchen " of the 



