436 KIOHARD EVANS. 



this cap of chromatin short processes pass along the inter- 

 zonal fibres for a short distance, thus giving them the appear- 

 ance of being thicker at the ends than in the middle. The 

 fibres during this and the previous stage are more distinct 

 than they are at any other time (fig. 42, 6 a, Qtb). The cap of 

 chromatin becomes gradually more uniform, and shows fewer 

 signs of its multiple origin from a number of chromosomes, 

 but the interzonal fibres still retain their sharp outline (fig. 

 42, 7 a, 7 b). 



The next change observable is the constriction of the cell. 

 The interzonal fibres, at the same time becoming much elon- 

 gated and attenuated, are difficult to make out, though lying 

 parallel with one another and still keeping their independence 

 (fig. 42, 8 a, 8 5). 



The chromatin presents, in some cases, a blotchy appearance, 

 while in others it shows signs of preparation for the final break- 

 ing up into granules. In the next stage the cell has become 

 completely divided, the daughter cells, however, being con- 

 nected with each other by means of a fine thread which consists 

 of the constricted remains of the interzonal fibres. The chro- 

 matin shows further signs of the final breaking up (fig. 42, 9 a, 

 9 b). 



Finally the two cells become separated, and all traces of the 

 fibres connecting the two masses of chromatin in the previous 

 stages have disappeared. The chromatin itself presents the 

 appearance of a granular blotch lying in a clear area, and 

 subsequently breaks up so as to produce the small granules 

 characteristic of the resting nucleus (fig. 42, 10 a). 



Appendix F. 



Technique. 



The colonies of Spongilla from which the larvae were 

 obtained were procured from the river Cherwell, in which 

 Spongilla grows in large quantities on the roots of the trees 



