436 



WATASE. 



[Vol. \'\U. 



As mentioned above, the size of the microsome varies, and, as 

 a general rule, becomes smaller as it lies nearer the periphery of 



the cell. There are, then, two 

 important facts to be noted, viz., 



I. The microsomes stain 

 exact<ly like the centrosomes, 

 and therefore both differ from 

 the cytoplasmic thread proper 

 in one common particular. 



2. The size of the microsomes 

 gradually increase as we pass 

 from the periphery of the cell 

 toward the centre of the aster. 



Two questions arise, viz., 

 Are not the centrosome and 

 the microsome essentially one 

 and the same thing.'* Is not 

 the reason why the centrosome 

 is larger than the rest, because 

 it is found at one end of the 

 linear series toward which the 

 size of the microsome gradually 

 increases .'' 



Considered purely from the 

 anatomical and the micro- 

 chemical side, I must answer 

 these questions in the affirma- 

 tive, and see no reason why the 

 centrosome can not be regarded 

 simply as a viicrosoine of gigan- 

 tic size. If this statement can 

 be maintained, then, the abso- 

 lute uniqueness claimed for the 

 centrosome as a cellular ele- 

 ment, must be given up, for as 

 is well known the microsome is 

 the universally distributed ele- 

 ment in the cytoplasm of animal 



Fig. 3. Blastomeres in one of the 

 radii in the blastodisc of Loligo feaiii, 

 showing the formation of the spindle 

 filaments from the centrosome. In 

 the segment (i), the nucleus is still 

 spherical, and no spindle rays are yet 

 distinctly visible ; in (2) the outline' 

 of the nucleus is flattened and the 

 spindle rays are distinctly visible ; in 

 (3) and (4) the increase in the bulk 

 of the spindle, and the corresponding 

 decrease in that of the nucleus go 

 hand in hand. 



