SECRETORY PHENOMENA IN SILK (iLAND. 425 



The substance which fills all available space in the lumen 

 not occupied by silk secretion, may well be similar in its properties 

 to mucus, lubricating the tube for the passage of the silk fiber. 

 No origin for this substance has been found. It does not appear 

 to be secreted by the cells of the gland, nor does it seem to be a 

 dislodged part of the bodies of the cells. 



DISCUSSION. 

 i. Relation of the Nucleus to Secretion. 



The nucleus and cytoplasm of the cells of the silk gland are 

 closely associated in the production of the silk secretion. By 

 many investigators, the nucleus has been considered the center 

 of secretory activity in that the nucleoli migrate from the nucleus 

 into the cytoplasm and there undergo modification. Study of 

 the silk gland cells of II. cunea has given further indication of 

 nuclear participation in silk production through the presence of 

 nucleoloid bodies. These nucleoloid bodies do not themselves 

 pass into the cytoplasm but appear to constrict pieces from their 

 periphery that increase in size within the nucleus, finally passing 

 through the nuclear wall into the cytoplasm where further 

 modification of their substance occurs. 



2. Relation of Mitochondria to Secretion. 



Mitochondria having a characteristic arrangement in the cyto- 

 plasm of the secreting region are present in great numbers. It 

 is quite possible that they take some part during the transitory 

 stage when the secretion droplets are present in the cytoplasm, 

 in modifying the material and transmitting it to the lumen. 

 Mitochondria may act as catalysts, as suggested by Emberger 

 ('25) or they may take a more direct part in secretion, but their 

 presence and orientation toward the lumen seem to indicate that 

 they are not passive cytoplasmic inclusions. Mitochondria are 

 present throughout the extent of the gland but in the middle 

 and anterior portions, they are shorter than in the secretory 

 portion and show little definite orientation. In these portions, 

 they may aid in the process of conduction and in general metabolic 

 activity. 



