3io 



SOME PROBLEMS OF CELL-ORGANIZATION 



the astral rays are thinner and stain less deeply than farther 

 out. Brauer's account is substantially the same, though no definite 

 " Heller Hof " was found, and the astral rays were traced directly in 

 to the boundary of the centrosome. He added, however, two impor- 

 tant observations, viz. (i) that the central granule is visible at every 

 period ; and (2) division of the centrosome is preceded by division of 

 the central granule (Fig. 148) an observation recently extended by 

 Boveri to the division of the egg-centrosome. 1 Van Beneden and 

 Neyt ('87), on the other hand, gave a quite different account of the 



E F G H 



tig. 152. Diagiciiiia illustrating various accounts of centrosome and aster. 

 A. Centrosome, a simple granule at the centre of the aster; ex. sperm-aster in various animals. 

 B. "Centrosome," a sphere enclosing a central granule or centriole; ex. Brauer's account of 

 spermatocytes of Ascaris. C Like the last, but " centrosome " surrounded by a " Heller Hof"; 

 ex. Boveri's account of the centrosome of the Ascaris egg. D. Central granule surrounded by a 

 radial sphere ("centrosome") bounded by a microsome-circle, and lying in a "Heller Hof"; 

 ex. polar spindles of Thysanozoon, Van der Stricht. E. Central granule (" centrosome ") sur- 

 rounded by medullary and cortical radial zones, each bounded by a microsome-circle ; ex. polar 

 spindle of Unio, Lillie. F. Van Beneden's representation of aster of the Ascaris egg; like the last, 

 but the " corpuscula central " consisting of a group of granules. G. " Centrosome," a group of 

 granules surrounded by a "Heller Hof"; ex. the echinoderm-egg. H. "Centrosome" (central 

 granule) surrounded by a vague larger body lying in a reticulated centrosphere ; ex. Thalassema. 

 [GRIFFIN.] 



structures at the centre of the aster. The " corpuscule central " 

 (usually assumed by later writers to be the centrosome), described as 

 a "mass of granules," is surrounded by two well-defined astral zones, 

 formed as modifications of the inner part of the aster, and constitut- 

 ing the "attraction-sphere." These are an inner "medullary zone," 

 and an outer " cortical zone," each bounded by a very distinct layer 

 of microsomes (Fig. 152, F). 



1 Reported by Fiirst, '98, p. ill. 



