228 SOME PROBLEMS OF CELL-ORGANIZATION 



other investigators have been unable to find a distinct body to be 

 identified as a centrosome within the centrosphere. As far as the 

 sea-urchins are concerned, there is, I think, good reason to doubt not 

 only my own former conclusions, but also those of Boveri. Both vom 

 Rath ('95, 2) and Hill ('95) find at the centre of the centrosphere in 

 sea-urchins a distinct black granule (" centrosome "), which becomes 

 double in the early anaphase precisely as in Tkalasscma. More- 

 over, Griffin's studies under my direction show that the minute single 

 centrosome of TJialassema entirely loses its staining-power after cer- 

 tain reagents and only comes into view after other treatment. 1 I am 

 now,' therefore, inclined to believe that many if not all of the accounts 

 asserting the absence of a minute central centrosome in the centro- 

 sphere are based on unsuitable methods, and that in most of such 

 cases, if not in all, it is really present. 



However this may be, it is now certainly known that the centro- 

 some is in some cases a granule so small as to be almost indistin- 

 guishable from the microsomes ; that in this form it is able to organize 

 the surrounding cytoplasm into the astral system ; and that in this 

 form it may be handed on by division from cell to cell. It may well 

 be that in some cases such a centrosome may multiply to form a cen- 

 tral group, as in leucocytes and giant-cells ; that it may enlarge to 

 form a granular or reticular sphere, as Boveri describes; and that 

 the individual granules within such a sphere do not have the value 

 of centrosomes. Such secondary morphological modifications do not 

 affect the physiological significance of the centrosome as a perma- 

 nent cell-organ, but they have an important bearing on the question 

 of its relation to the other constituents of the cell. 



The latter question has not been definitely answered. Biitschli, 

 who has been followed by Erlanger, regards the centrosome as a 

 small differentiated area in the general alveolar structure ; and he 

 describes it in the sea-urchin as actually made up of a number of 

 minute vesicles (Fig. 8, B). Burger ('92) suggested that the entire 

 attraction-sphere and aster arise by a centripetal movement of micro- 

 somes to form a radiating group the centre of which (centrosome) is 

 represented by a condensed mass of the ground-substance. Watase 

 ('93, '94) added the very interesting suggestion that the centrosome is 

 itself nothing otJier than a mici'osome of the same morphological 

 nature as those of the astral rays and the general thread-work, differ- 

 ing from them only in size and in its peculiar powers. 2 Despite the 



1 The centrosome disappears after fixation with sublimate-acetic, but is perfectly shown 

 after pure sublimate or picro-acetic. See Science, Jan. 10, 1896. 



' 2 The microsome is conceived, if I understand Watase rightly, not as a permanent mor- 

 phological body, but as a temporary varicosity of the thread, which may lose its identity in 

 the thread and reappear when the thread contracts. The centrosome is in like manner not 

 a permanent organ like the nucleus, but a temporary body formed at the focus of the astral 



