GENERAL CONCLUSIONS. 47 



chromatin which have the power of moving about in the net- 

 work. These chromatic granules are fairly uniformly diffused 

 in the resting nucleus, but in a nucleus preparing to divide 

 they aggregate together in certain parts of the network. The 

 parts of the network from which the chromatin has gone 

 become inconspicuous and form the achromatic spindle-fibres, 

 while the parts into which it has gone form the conspicuous 

 deeply-staining rod-like fibres, so characteristic of a dividing 

 nucleus. The achromatic fibres of the spindle which begin to 

 appear at the first sign of the division of the nucleus are, on 

 this view, parts of the nuclear network. With this view I 

 entirely agree. The structure of the various phases of the 

 nucleus of the ovum of Peripatus will bear the same explana- 

 tion, allowing for this difference, viz. the amount of chromatic 

 substance in the ovum of Peripatus is much smaller — so small, 

 indeed, that even in the resting stage (PI. Ill, fig. 8) the 

 chromatin is absent from the greater part of the network, which 

 thus has the pale appearance of the achromatic fibres of Flem- 

 ming, an appearance which is only found in the dividing nuclei 

 of the salamander. The reason why achromatic fibres are so 

 little marked in the resting nuclei of most animal cells is that 

 they are masked by the large amount of chromatic substance 

 they contain. 



This view of the spindle-fibres is not at all opposed to 

 Strasburger's contention (15, fig. 44) that part of them are de- 

 rived from the extra-nuclear spongework ; for the nuclear and 

 extra-nuclear spongework are, as I have already maintained, 

 continuous with each other; in other words, part of the same 

 system. 



I have seen nothing of any process corresponding to the 

 splitting of the fibres ; but this is not to be wondered at con- 

 sidering that I have only twice found the spindle stage of the 

 nucleus. 



B. It is becoming more and more clear every day that 

 the cells composing the tissues of animals are not isolated units, 

 but that they are connected with one another. I need only 

 refer to the connection known to exist between connective 



