208 THE CELL 



place in a lymph cell during the course of three hours, the pre- 

 paration being kept at a temperature varying from 16 to 18 . 

 Arnold (VI. 1) and others have verified his statements, and have 

 amplified them in various ways. The vesicular nucleus can change 

 its form actively, and can cover itself with excrescences and pro- 

 tuberances. Under such circumstances constrictions frequently 

 occur, after which the nuclei break up into two, three, or more 

 pieces (Fig. 100 A, B). The nuclear fragments move apart 

 from one another, not infrequently remaining joined together for 

 a considerable time by delicate connecting threads. Cell division 

 often closely follows nuclear division, as is seen in Figs. 100 A, 13. 



FIG. 100. A A migratory cell from a disc of elder pith which has lain for ten days in 

 the lymph sac of a Frog. When first observed the nucleus was somewhat constricted in 

 its middle, whilst its ends were bilobed. After five minutes the nuclear division was com- 

 pleted (after Arnold, PI. XII., Fig. 1). B Migratory cell during division. Fig. A de- 

 veloped into Fig. B during the course of thirty minutes (after Arnold, PI. XII., Fig. 3). 



The protoplasmic body also becomes constricted between the 

 nuclear fragments, which move apart, but are still joined by a 

 fine thread. The two nuclear fragments move in opposite direc- 

 tions by means of a large number of amoeboid processes. In 

 consequence, the connecting bridge between them is sometimes 

 drawn out to a long fine thread, after the daughter-nuclei have 

 separated from one another. 



" No law can be laid down as to the time when the various 

 stages of division follow one another during fragmentation ; very 

 frequently nuclei and cells linger in one or other stage " (Arnold). 



