THE ARCIIOPLASMIC STRUCTURES 32 I 



formation of the rays was Driiner, who maintained in the case of the 

 mitosis of salamander testis-cells, that "not a sin^de fibre of the astral 

 system of the mother-cell is carried over unchan<;ed into the orj;anism 

 of the daughter-cell" ('95, p. 309)- The same conclusion was soon 

 afterward supported by Braus ('95) in the case of the cleava<;e- 

 mitoses of Triton. The most convincing evidence of this fact has 

 been given by studies on the maturation and fertihzation of the egg 

 by Grifhn ('96, '99), MacFarland ('97), Lillie ('99), and Coe ('99), all of 

 whom find that the new astral centres, arising by division of the cen- 

 trosome, move away from the old position, to lu/iic/i, hoivcvcr, the old 

 rays still converge ivhile the new asters are independently forming 

 (Fig. 155). This is shown with especial clearness in the i^g'-^ of Cere- 

 brattilus (Coe), where the peripheral portions of the old asters persist 

 until the new amphiaster is completely formed. This observation 

 seems conclusively to overturn Kostanecki's hypothesis of the persist- 

 ence and division of the rays, and together with the work of MacFar- 

 land gives a very strong support to Boveri's later view. 



It still remains an open question whether the rays actuallv arise 

 from the substance of the centrosome, from a specific surrounding 

 archoplasm, or by differentiation out of the general substance of the 

 meshwork. The first of these possibilities has been urged in a very 

 interesting way by Watase ('94), who believes that the centrosome 

 "spins out the cytoplasmic filaments"^ of the spindle and aster, and 

 that ordinary microsomes may in Hke manner spin out the fibril la- of 

 ordinary cytoplasmic networks.^ This view is sustained by the mode 

 of origin of the axial filament in the spermatozoa and that of the cilia 

 in plant spermatozoids. It is, on the other hand, opposed by the 

 almost infinitesimal bulk of the centrosome as compared with that of 

 the aster that may form about it, and by the formation of the spindles 

 in higher plants in the apparent absence of centrosomes. On the 

 whole, the facts do not seem at present to warrant the acceptance of 

 Watase's ingenious hypothesis, and the most probable view is that 

 of Driiner and Boveri, that the rays are differentiated out of the walls 

 of the meshwork. In cases where the protoplasm is reticular or 

 fibrillar the differentiation of the ravs mav be indistinguishable from 

 a mere rearrangement of the thread-work ; in alveolar protoplasm 

 they may be seen as new formations, while in either ca.se the 

 material of the old aster may be more or less directly utilized in the 

 building of the new. The feature common to all is the periodic 

 activity either of the centre itself or of the surrounding protoplasm, 

 and the coincidence or non-coincidence of the new aster with the old 

 is apparently a secondary matter. 



1 I.e., p. 283. 



2 See the same paper for a suggestive comparison of the astral librilLv to muscle-fihrcs 



