PHYSIOLOGY OF THE NUCLEOLI 63 



''In many places, the nuclear membrane is quite difficult to 

 distinguish, being lost in the adjacent cytoplasm; this is espe- 

 cially true in the nuclei along whose outer border the dark 

 cytoplasmic areas are numerous" (after one hundred and twenty 

 hours of activity). 



". . . . These (the areas of darkened cytoplasm) are 

 here mostly in close proximity to the outer boundary of the 

 nucleus, but exceptionally present along the inner border of 

 the nucleus" (after an activity of two hundred and forty hours). 



Their so-called "darkened areas of cytoplasm" are practi- 

 cally identical with what I consider as the nucleolar material 

 extruded into the cell-body or remaining in the nucleus but 

 ready to migrate. They attempted no explanation of the 

 significance of the appearance of the "darkened areas of cyto- 

 plasm." If my interpretation be correct, there is rio doubt that 

 ten years ago they observed the phenomenon of the migration 

 of the nucleoli in the silk-gland cell of caddis-worms. 



The case of the migration of the nucleoli in the silk-gland cells 

 of caddis-worms supports the theory that the extruded nucleolar 

 material is metabolized into the secretion products, since the 

 granules, which are the migrated nucleoli, are in such large num- 

 ber as to render it rather improbable that they represent a 

 degenerating product, and since, moreover, the quantitative 

 relation of the granules to the different physiological conditions 

 of the cell is such as to be naturally expected for the material 

 prepared for secretion. 



c. Summary. The foregoing observations on Pieris and 

 Neuronia seem to justify the following statements as regard the 

 morphological changes of the nucleoli in the silk-gland cells of 

 the insects studied: 



1. The nucleoli multiply by division of the preexisting ones, 

 and they increase in amount as the gland becomes more 

 functional. 



2. Before the gland becomes functional, a portion of the 

 nucleoli begins to migrate from the nucleus in considerable 

 number into the cell-body. 



