12 i Art. 3.— N.;ohide Yatsu : 



that in tlie end ii bridge- was formed between the two blastomeres. 

 The bridge was not cut through. One case of this peculiar 

 mode of cleavage was the result of a horizontal section. In the 

 other two, the curving of the furrow faced the side of more 

 ■cytoplasm (in Fig. 41, PI III to the left). Conklix observed in 

 the egg of Linenjes iiiercwiu^ tlie turning-up of the cleavage furrow 

 v(Pl. 3, fig. 13) and thought it probable that this might l)e due to 

 the flowing of cytoplasm through the bridge from one cell to the 

 other (p. 160). In the Beroc, egg no streaming phenomenon ac- 

 ■companies this curling-up of the cleavage furrow. 



In two cases for some unknown reason tlie division stopped at 

 .a certain stage and <lid not cut thi-ough. In one case at tlie begin- 

 ning of the division the '' cleavage head " Avas thick but as it pro- 

 •€eeded the ectoplasm thinned out somewhat (PI. Ill, Figs 43, 44). 



From this experiment it may be concluded that after the 

 " cleavage head " is established, the cell-division is accomplished 

 without the instrumentalitv of either the uncleus or the centro- 

 somes. Furthermore it should be noted in this experiment that 

 there is no perceptible difference between the cut and the uncut 

 -eggs in the thickness of "cleavage head," though in some cases 

 .a little retardation of the progress of the cleavage is seen in 

 the cut eggs. The up-and-lown flow of the ectoplasm takes place 

 independently of the presence or absence of either the nucleus or 

 the centi'osome. 



d) Expeiiment. II' (Six cases). 



In order to test whether either the nucleus or the centrosome 

 •exerts any influence on the deepening cleavage furrow, the 

 nucleated portion of one side was cut off at various angles and 

 periods, and the behavior of the cleavage furrow was studied. 



In all cases division took place undisturbed by the operation 

 '(PI. Ill, Figs. 45, 46). In one case, however, the cleavage furrow was 

 bent near its end towards the nucleated side, but such a bending 

 occurs so often in eggs not operated upon (Fig 11 PI. 1) that the 

 •cause of the bending in this particular case cannot be ascribed to 

 the operation. 



