714 SUMMABY OF CUKKENT BESEARCHES RELATING TO 



found to be associated with the same definite arrangement of the 

 segments in the nucleus, and it may either precede or succeed the 

 arrangement of the segments into the nuclear plate. 



If we compare what is now Ijnown as regards plants with the 

 results of studies on the division of the nuclei of animals we find 

 that, with one exception, there is really no important difference 

 between them. The investigation of plants shows that the spindle- 

 shaped fibres almost certainly arise from compressed cytoplasm. The 

 whole fxamework of the nucleus is to be found in the filamentar coils, 

 while the nuclear cavity is only filled by homogeneous nuclear fluid. 

 The whole mass of spindle-shaped fibres have their origin in the 

 cytoplasm. 



The difference in the way in which cell-division is completed is a 

 point of distinction between animals and plants, but it does not obtain 

 in the lowest forms of either kingdom. The formation of the con- 

 nective filaments in the separation of the cell-body is a distinctive 

 characteristic of plants ; but, notwithstanding this, the result of cell- 

 division is the same in both plants and animals. 



In both we find that in the " prophases " of nuclear division cyto- 

 plasm is collected at the future poles of the cell-nucleus; this 

 phenomenon is often very striking in animal-cells, and is especially 

 well marked in ova. The nucleus becomes provided with two 

 radiating systems, even before any dicentric arrangement can be 

 detected in the cell-nucleus. The observations which the author has 

 made lead him to think that the spindle-shaped fibres derived from 

 the cytoplasm have a directive influence on nuclear division ; the 

 frequently simultaneous division of nuclei in multinucleated cells may 

 be easily supposed to be due to this influence and the surrounding 

 cell-plasma. 



Strasburger thinks that some of the aberrant forms of division 

 noted by Flemming may be explained by what he has seen in plants. 

 The tub-shaped figures which become apparent during the arrange- 

 ment of the segments in the testicular epithelium of the salamander 

 call to mind what was seen in the embryo-sac of Friiillaria, and 

 suggests that an explanation is to be found in the divarication of the 

 daughter-segments on one side, and their approximation to one another 

 on the other. In the red blood-cells of Salamandra the cell-nucleus 

 becomes considerably enlarged during the development of the fila- 

 mentar coil, and a large amount of cell-substance is taken up into the 

 nuclear figure. If the spindle-shaped fibres form only a small figure 

 in the cell, it would be clear that all the cytoplasm was not used up 

 in forming this figure, and we should have a case similar to that seen 

 in the pollen-mother-cells of Fritillaria persica, where in the first act 

 of division granular cytoplasm is found between the spindle-shaped 

 fibres. 



The ideas now derived from a study of animals and plants cannot be 

 directly applied to the Protista, where the separate parts of the cell- 

 body often undergo great changes and become adapted to new functions ; 

 we must greatly increase the number of our observations before we 

 can hope to arrive at generalizations of universal value. 



