210 



THE CELL 



into several portions (Fig. 102 C). As the disintegration pro- 

 gresses, it may be broken up into a larger number of smaller 



FIG. 102. A Side view of a perforated nucleus from the Ij-mphatic peripheral layer of 

 the liver of Triton alpestrin. The nucleus is flattened in the direction of the perforation 

 (after Goppert, PI. XX., Fig. 4). B Perforated nucleus with distinct radial arrangement 

 of the nnclein framwork (after Goppert, PI. XX., Fig. 4). C Ring-shaped nucleus of 

 a lymph cell divided into several portions by constrictions (after Goppert, PI. XX., Fig. 10). 



nuclei, which are sometimes connected for a long time by delicate 

 connecting bridges. Similar " perforated nuclei" have been ob- 

 served in other objects by Flemming (VI. 16) ; for instance, in the 

 epithelium of the Frog's urinary bladder. However, in this case, 

 division of the cell body does not appear to occur. 



Direct nuclear division occurs also occasionally in the vegetable 

 kingdom. Certain objects, like the long internodal cells of the 

 Characeae, or older cells of more highly organised plants, are most 

 suitable for observing it ; thus Strasburger (II. 41) observed in 

 the older internodes of Tradescantia more or less irregular nuclei 

 which are divided into portions of varying size and shape. " If 

 the indentation is one-sided, the cell nuclei appear kidney-shaped ; 

 but if they are indented all round, they look biscuit-shaped, or 

 irregularly lobulated. In many cases the fragments have quite 

 separated from one another, either still remaining in contact, or 

 lying at a greater or less distance from one another. These 

 nuclear fragments may number as many as eight to ten in one 

 cell." In Characeae the nuclei may temporarily assume the 

 appearance of a string of pearls in consequence of several con- 

 strictions having occurred. This appearance passes away when 

 the fragmentation is completed. 



However, even if constrictions of the nucleus are observed, it 

 cannot be immediately taken for granted that direct division is 

 commencing, unless this method of multiplication has been already 

 observed in all its stages in the object in question. Thus in ova 

 and in sperm-mother-cells, mulberry-shaped or irregularly 



