PHYSIOLOGY OF THE NUCLEOLI 59 



the granules we have just observed. The granules of the mi- 

 grated nucleoh increase in amount as the de^'elopment advances, 

 and, in a little older larva, the entire of the cytoplasmic area is 

 filled with the granules (fig. 3). 



In the larva a Httle older than those considered above (fig. 4), 

 a mass of the secreted substance occurs in the lumen of the 

 gland. It is apparent, therefore, that the gland is already func- 

 tional at this stage. Here the nucleus begins to show its branch- 

 ing, and the amount of the chromatin and of the nucleolar ma- 

 terial seem to have been increased. The process of the multi- 

 pHcation of the nucleoh is apparently proceeding rapidly. Along 

 the border of the nucleus and the cell-body are many masses 

 of the nucleolar material, indicative of the rather rapid process 

 of nueleoli migration occurring (fig. 5). 



The cytoplasmic area shows some elongate vacuoles of vary- 

 ing sizes (fig. 4). Gilson ('90), working on the silk-glands of 

 various lepidopterous larvae, found vacuoles present in the cell- 

 body and also in the nucleus of the cell, and he interpreted them 

 as containing secretory material. Matheson and Ruggles ('07) 

 stated in their work on the siinilar glands of Apanteles glomeratus 

 that "numerous vacuoles are present in the cytoplasm, becom- 

 ing most abundant during the time of glandular activity," and 

 that 'Hhe contents of the vacuoles remain unstained by any of 

 the coloring agents used." Such vacuoles have been observed 

 also in the silk-glands of caddis-worms, not only by Gilson ('96), 

 but also by Marshall and Vorhies ('06), but the latter authors 

 do not think that they contain secretory material. Their ob- 

 servations would show that the cytoplasm in the normal gland 

 cell ''presents an appearance free from vacuoles," while after 

 the activity of the gland for two and one-half hours, "a num- 

 ber of fairly large vacuoles are seen along, the outer margin of 

 the cell, and such vacuoles persist in the cell-body of the gland 

 which has been active for longer periods (at least up to 250 

 hours)." 



It is rather inconceivable that the amount of the secretion 

 material (supposed to be contained in the vacuoles) in the cell 

 increases, instead of decreases, after the cell has discharged, 



