THE ARCHOPLASMIC STRUCTURES 23 I 



polar corpuscle (centrosome) and the rays extending from it, includ- 

 ing the achromatic fibrils of the spindle, are the result of the appear- 

 ance in the egg-protoplasm of two centres of attraction comparable 

 to two magnetic poles. This appearance leads to a regular arrange- 

 ment of the reticulated protoplasmic fibrils and of the achromatic 

 nuclear substance with relation to the centres, in the same way that 

 a magnet produces the stellate arrangement of iron filings."^ 



This view is further developed in Van Beneden's second paper, 

 published jointly with Neyt ('87). ''The spindle is nothing but a 

 differentiated portion of the asters." ^ The aster is a "radial structure 

 of the cell-protoplasm, whence results the image designated by the 

 name of aster." ^ The operations of cell-division are carried out 

 through the " contractility of the fibrillae of the cell-protoplasm and 

 their arrangement in a kind of radial muscular system composed of 

 antagonizing" groups." "^ 



An essentially similar view of the achromatic figure has been 

 advocated by many later workers. Numerous observers, such as 

 Rabl, Flemming, Carnoy, Watase, Eismond, Reinke, etc., have ob- 

 served that the astral fibres branch out peripherally into the general 

 reticulum and become perfectly continuous with its meshes. This is 

 very clearly shown in the formation of the sperm-aster about the 

 middle-piece of the spermatozoon. In the sea-urchin {Toxopncnstcs) 

 the formation of the rays from the cytoplasmic reticulum can be fol- 

 lowed step by step, and there can, I think, be no doubt that the astral 

 rays arise by a direct transformation or morphological rearrangement 

 of the pre-existing structure, and that they extend themselves at their 

 outer ends, as the sperm-aster moves through the egg-substance, by 

 progressive differentiation out of this reticulum.^ Once formed, how- 

 ever, the rays may possess a considerable degree of persistence and 

 may actively elongate by growth. Only thus can we explain the 

 pushing in of the nuclear membrane by the ingrowing spindle-fibres 

 during the prophases of mitosis in certain forms (p. 50) and the 

 bending of the rays when two asters collide, as recently described by 

 Kostanecki and Wierzejski ('96). It seems certain, furthermore, that 

 during the rotation of the amphiaster in the formation of the polar 

 bodies (Fig. 71) and in similar cases, the spindle, at lea.st, moves bodily. 

 The substance of the spindle or of the asters may, moreover, persist 

 in the resting cell, after the close of mitosis, as the attraction- 

 sphere or paranucleus (Nebenkern), and in such cases the term 

 " archoplasm " may conveniently be retained for descriptive purposes. 

 To regard the archoplasm as a primary and independent constituent 

 of the cell would, however, as I believe, be an error. 



1 '5 



3, p. 550. - I.e., p. 263. 3 i_c_^ p. 275. * I.e., p. 280. 5 '95, 2, p. 446. 



