REGENERATION IN LUMBRICULUS. 3OI 



that the nucleolus bears some relation to the activity of the cell 

 body and nucleus. Many cases have been reported of nucleolar 

 extrusions preceding the formation of yolk granules. Ludford 

 ('22) also reports that in the more active cells of the endoderm 

 of Limnaea the nucleoli are larger than in those of the hypodermis. 

 He is "inclined, therefore, to regard the size of the nucleolus as 

 an indication of the degree of metabolism existing in the cells 

 the greater the metabolic activity, the larger the total volume 

 of nuclear (nucleolar ?) matter present in the nucleus, or extruded 

 into the cytoplasm" (p. 139). Wilson ('25, p. 96) also believes 

 that there is a "question whether the nucleolus may not play a 

 more active and important part in cell metabolism than most 

 writers have hitherto assumed." 



An examination of slides of Lumbriculus, both of uninjured and 

 of regenerating individuals reveals no cases of nucleoli which 

 could be interpreted as being extruded into the cytoplasm from 

 the nucleus. There is considerable evidence, however, that 

 nucleolar size is in some manner an indication of the degree of 

 metabolic activity of the cell. 



In uninjured worms the gut cells of the first eleven or twelve 

 segments have small nucleoli. Similarly those for some distance 

 from the anal opening have a comparatively small amount of 

 nucleolar substance. In the intermediate portion, however, rela- 

 tively large nucleoli are present. The cells of the mouth cavity 

 and esophagus naturally do not take as great a part in the 

 digestive processes as do those found more posteriorly. In the 

 mid-gut the digestive fluids are being poured into the lumen and 

 the food is being absorbed. Consequently considerable cell 

 activity is necessary. Toward the posterior end such activity 

 naturally drops off again. The size of the nucleoli, therefore, 

 parallels more or less the extent of the activity expected of the 

 cells in the various regions of the gut (p. 281). 



Furthermore, in the case of the setigerous glands, the nucleoli 

 of the cells are large in the growing tail region and in a re- 

 generating bud where the new setae are being rapidly formed 

 (pp. 281 and 291). In the old segments of a worm, however, 

 where the setae have been present for a considerable time, the 

 nucleoli are usually small (p. 281). The cells in the active 



