THE ARCHOPLASMIC STRUCTURES 



233 



Nereis, by Ruckert in Cyclops, and in a number of other cases, the 

 centrosphere has a non-radiate reticular structure (Figs. 71, 108, E). 

 In some cases no centrosome has been found in this sphere ; but for 

 reasons already stated (p. 228) I incline to believe that a centrosome 

 is really present. 



In many, if not in all cases of both types, the sphere consists of an 

 outer and an inner zone, the latter enclosing the centrosome ; but the 

 relation of the inner zone to the centrosome still remains, in a meas- 



Fig. 108. Diagrams illustrating various descriptions of centrosome and centrosphere. 

 A. Simplest type; only a minute ctntrosome at the focus of the ravs (sperm-aster in many 

 forms). B. Rays proceeding directly from a centrosome of considerable size within which is a 

 central granule. Example, Brauer's description of the spermatocytes of Ascaris. C. Rays pro- 

 ceeding from a clear centrosphere (astrosphere of Strasimrger), enclosing a centrosome like 

 the last but with no central granule (in flowering plants according to Guignard, Strasburger, 

 and others). D. An extremely minute centrosome lying in the middle of a large reticulated cen- 

 trosphere (eg. Hill's description of the sperm-aster in sea-urchins and tunicates). E. Like the 

 last, but with a small spherical body surrounding the centrosome (examples, the eggs of Thalas- 

 seiiia and Nereis}. F. No centrosome as distinguished from the reticulated centrosphere. Ex- 

 amples in the pigment-cells of fishes according to Zimmerman, in the eggs of echinoderms ac- 

 cording to Wilson; many similar accounts have been given, but all are open to question. G. In 

 Ascaris, according to Van Beneden, outside the centrosome lie the cortical and medullary zones 

 of the attraction-sphere. H. The same according to Boveri. The centrosome contains a cen- 

 tral granule or centriole (cf. B.) ; outside this is a clear zone (medullary zone of Van B'-neden), 

 and outside this a vaguely defined granular zone, probably corresponding to Van Beneden's 

 cortical zone. 



ure, in doubt. Van Beneden described the centrosphere in A scan's 

 as consisting of an outer cortical and an inner medullary zone, both 

 of which were conceived as only a modification of the inner region of 

 the aster. Boveri's account is somewhat different. The centrosome 

 is described as surrounded by a clear zone (" heller Hof "), probably 

 corresponding with Van Beneden's "medullary zone," while the 

 " cortical zone " of the latter author is not recognized as distinct from 

 the aster (or archoplasm-sphere). The centrosome itself contains a 



