No. 2.] THE SEA-URCHIN EGG. 445 



gated into a spherical granular mass (equivalent to the "attrac- 

 tion-sphere " of Van Beneden), as the result of an attraction 

 exerted upon it by the centrosome (p. 70). The entire achro- 

 matic division figure (amphiaster) is derived from this mass, 

 which divides into two, while from each of the resulting prod- 

 ucts rays grow out into the cell-substance, some of them be- 

 coming attached to the chromosomes and forming the spindle- 

 fibres, while others give rise to the radiating astral fibres (p. 81). 

 At the close of the karyokinesis the archoplasm-fibres are again 

 withdrawn into the central mass, breaking up into granules 

 meanwhile (p. 128), so that each daughter-cell receives one-half 

 of the entire archoplasmic material of the mother-cell. 



Boveri was careful to guard against the view that the archo- 

 plasmic rays extend themselves during the formation of the 

 amphiaster by progressive differentiation at their free ends, 

 out of cell-material other than the specific archoplasm-material 

 preexisting as such. He believed, on the contrary, that he 

 had obtained conclusive proof that the rays were formed ex- 

 clusively out of the substance of the archoplasm-sphere (p. 79), 

 and even went so far as to accept the probability that the 

 archoplasmic microsomes, out of which the rays are formed 

 and into which they again are resolved at the close of karyoki- 

 nesis, possess a distinct morphological individuality that is never 

 lost throughout the entire cycle of cell-division (p. 80). 



The same general conception is adhered to in the recent 

 paper on the sea-urchin cited above (p. 443), but with one im- 

 portant modification. Ascaris, namely, is now admitted to be 

 an exceptional case, and Boveri is inclined to the view (which, 

 however, is very cautiously expressed) that in most cases the 

 archoplasmic fibres (" Radien ") may be " ganz neue Organisa- 

 tionen " — "die aus dem Substanzengemenge des Protoplasma 

 gleichsam auskrystallisieren " ,(/. c, p. 40). However this may 

 be, the asters cannot be regarded as arising by the morpho- 

 logical rearrangement of a preexisting reticulum or alveolar 

 structure as maintained by Butschli, Heidenhain, Reinke, Eis- 

 mond and other authors; and in the case of Ascaris, at least, 

 Boveri finds himself justified in the positive assertion that the 

 granular archoplasm-.sphere and the aster derived from it are 



