488 THOMAS H. BRYCE. 



similar conditions^ the sperm ceutrosonie be present, the cyto- 

 ceutruin remains latent. The centrosome looked at in this 

 way, is not a specific cell organ in the sense that it must 

 consist of a specific chemical substance, but that parts of a 

 substance contained in the nucleus, undergoing certain 

 changes, and grouping themselves together, are organised 

 into a centrosome. 



Thus the ovocentrum of the sea-urchin egg is not to be 

 considered an individualised centrosome, but an intra- 

 nuclear latent cytocentrum, and the nucleus is a centro- 

 nucleus. Thus the centrosome in such a case is not some- 

 thing strictly new, but arises by the transformation in a 

 definite manner of a cytocentrum already present. It is a 

 case not of new formation, but of " reparation." " Gervisse 

 Centronuclei sind im stande unter bestimmten Bedinguugen 

 Centrosomen zu reparieren." 



Morgan's artificial astrospheres he did not admit to have 

 true centrosomes — the essential character of capacity for 

 division was not proved for them. 



This brings me to Wilson's very interesting and important 

 paper on the morphological phenomena in parthenogenetic 



The main results are that under the influence of the 

 magnesium chloride solution, not only are asters produced 

 de novo in connection with the nucleus, but also in the 

 cytoplasm. " Not only the asters connected with chromo- 

 somes (nuclear asters), but also the supernumerary asters 

 unconnected with nuclear matter (cy tasters), may multiply 

 by division ; the cytasters contain deeply staining central 

 granules indistinguishable from centrosomes, that divide 

 to form the centres of the daughter asters. These asters 

 operate with greater or less energy as centres of cyto- 

 plasmic division. Typical cytasters, often containing deeply 

 staining central granules resembling centrosomes, are formed 

 in the magnesium solution in enucleated egg fragments 

 produced by shaking the unfertilised eggs to pieces, and 

 these asters likewise may multiply by division, though 



