THE ARCHOPLASMIC STRUCTURES 229 



ambiguity of the word " microsome " Watase's suggestion is full of 

 interest, indicating as it does that the centrosome is morphologically 

 comparable to other elementary bodies existing in the cytoplasmic 

 structure, ,and which, minute though they are, may have specific 

 chemical and physiological properties. 



F. THE ARCHOPLASMIC STRUCTURES 

 I. Asters and Spindle 



The asters and attraction-spheres have a special interest for the 

 study of cell-organs ; for these are structures that may divide and 

 persist from cell to cell or may lose their identity and reform in suc- 

 cessive cell-generations, and we may here trace with the greatest 

 clearness the origin of a cell-organ by differentiation out of the struct- 

 ural basis. Two sharply opposing views of these structures are now 

 held. Boveri ('88, 2), who has been followed in a measure by Stras- 

 burger, maintains that the attraction-sphere of the resting cell is com- 

 posed of a distinct substance, " archoplasm? consisting of granules 

 or microsomes aggregated about the centrosome as the result of an 

 attractive force exerted by the latter. From the material of the 

 attraction-sphere arises the entire achromatic figure, including both 

 the spindle-fibres and the astral rays, and these have nothing to do 

 with the general reticulum of the cell. They grow out from the 

 attraction-sphere into the reticulum as the roots of a plant grow into 

 the soil, and at the close of mitosis are again withdrawn into the cen- 

 tral mass, breaking up into granules meanwhile, so that each daugh- 

 ter-cell receives one-half of the entire archoplasmic material of the 

 parent-cell. This material is, however, wholly distinct from that of 

 the general reticulum, not, as many earlier observers have maintained, 

 identical with it. Boveri was further inclined to believe that the 

 individual granules or archoplasmic microsomes were " independent 

 structures, not the nodal points of a general network," and that the 

 archoplasmic rays arose by the arrangement of these granules in 



rays. Once formed, however, it may long persist even after disappearance of the aster and 

 serve as a centre of formation for a new aster. In the latter case the astral rays are con- 

 ceived as actual derivatives of the centrosome which, as it were, spins them out in the cyto- 

 plasm. " The aster, from this point of view, may be considered as a physiological device 

 for concentrating the cytoplasmic substance in a form which can be spun out again into 

 filaments in the direction which will produce a definite physiological effect" ('94, p. 284). 

 This part of Watase's conception is, on the whole, I think, opposed to the facts, though it 

 certainly explains the inpushing of the nuclear membrane during the prophases of mitosis. 

 It is impossible to believe that the rays of the enormous sperm-aster are developed out of 

 the minute granule at their centre or that they flow back into it at the close of division. 

 The centrosome increases in size during the formation of the aster, decreases during its 

 disappearance, which is the reverse of what the hypothesis demands. Many other argu- 

 ments in the same direction might be urged. 



