570 
C. F. U. MEEK. 
hand, attributed cell division to the influence of a local 
thickening upon the surrounding cytoplasm. 
In 1897 Erlanger put forward a theory similar in certain 
respects to that of Rhumbler. His researches upon Cepha- 
lopod cells and Echinoderm ova led him to believe that the 
aster, under centrosome influence, exercises a chemical or 
physical attraction upon the cytoplasm. He said that during 
the prophase of mitosis the nucleus absorbs fluid from the 
surrounding- cytoplasm, and that its membrane disappears 
when a maximum volume is reached ; fluid is then with- 
drawn by the astei-s, particularly from the nucleus, whose 
achromatic substance is thereby converted into a spindle ; 
later the asters give up to the daughter-nuclei the fluid 
previously absorbed, and consequently diminish until they 
finally disappear in the resting stage. In the same year 
Kostanecki, who regarded the centrosome merely as an organ 
of insertion, suggested that the monocentric aster is con- 
verted into the spindle by longitudinal cleavage of its 
rays ; but this has not been corroborated by subsequent 
investigation. 
Following the researches of Mottier, Osterhaut, , and 
Strasburger, who denied the presence of centrosomes in 
Pteridophyta and Phanerogams, R. Hertwig published in 1898 
the result of his investigations upon ActinospliEei-ium. He 
believed that the central spindle is derived from the nucleus, 
and the asters from the cytoplasm ; and affirmed that through- 
out the animal kingdom changfes in form of the nucleus 
during mitosis repi-esent a process of growth, and are caused 
by forces arising within it. Although denying that nuclear 
elongation is caused by contractile fibres, he did not exclude 
the possibility of contraction in mitosis ; and thus agreed with 
Meves, who said that we must determine whether at a given 
moment a particular fibre causes movement by contraction or 
elongation. Moreover, Calkins and Ishikawa adopted the 
view that centrosome divergence is due to growth of the 
central spindle ; and the former, wdio agreed witliR. Hertwig 
regarding the origin of the metazoan centrosome, affirmed 
