230 BIOLOGICAL LECTURES. 



of the Protozoa. Recent observations lead to the view that it is 

 not a permanent organ of the cell (Brauer, Hertwig, Schaudinn, 

 Morgan, etc.), while its complete absence in higher plants and its 

 appearance in certain mitoses while absent in others of the same 

 species (Actinosphczrium) justify Flemm ing's view that centro- 

 somes may be present in mitosis, but not necessary for it. The 

 origin of the body, which in various cases is called the centro- 

 some, is equally unsatisfactory. Hertwig's and Balbiani's view, 

 that it comes from chromatin which may (Actinosphcerium) or 

 may not (Spirochona) become extranuclear, is opposed by the 

 views, often hypothetical, of many observers upon centrosomes 

 in Metazoa. Further and guarded observations, especially 

 among the Protozoa, must be made before the various con- 

 flicting views can be reconciled. 



COLUMBIA UNIVERSITY, 



December i, 1899. 



