SKCRIiTORY IMIKNOMKNA IX SILK GLAND. 419 



layei which is a modified secretion of the outer body wall and 

 is, in consequence, shed at each moult. The fine canaliculi are 

 arranged perpendicular to the surface and are interpreted to 

 serve as conduction paths through the cuticular intima for the 

 liquid secreted by the cells to the lumen. Blanc ('89) working 

 on the silk gland cells of Bombyx mori concluded that the intima 

 was a chitinous structure composed of very fine parallel threads 

 encircling the lumen at intervals of from 3-4 micra and showing 

 occasional anastomosis. Gilson ('94) confirmed the observations 

 of Blanc. Maziarski ('n) describing the intima, pictures the 

 structure as a thin membrane composed of a great number of 

 filaments passing in spiral lines around the lumen of the canal 

 and joined by fine transverse fibrillae, thus producing the appear- 

 ance of a network of threads. These filaments are described as 

 staining deeply with iron hsematoxylin and having the appearance 

 of rigid fibrils located in the protoplasm of the cell nearest the 

 lumen, and were thought to resemble organs of support but not 

 to serve as passageways for substances elaborated in the cells. 



Tanaka ('u) describes the intima as a striated, filamentous- 

 appearing structure of chitinous nature, thickest in the anterior 

 division and thin in the middle region. The filamentous stri- 

 ations appear to have a parallel arrangement except toward the 

 posterior region where anastomosis may occur. This chitinous 

 substance which gives rise to the intima is thought by Tanaka to 

 be secreted in the anterior region and never to undergo ecdysis, 

 but rather is added to in thickness with age. This is (p. 16), 

 he concludes, "a fact which goes a long way in proving the 

 secretion of this chitinous substance throughout the whole larval 

 life." 



Yamanouchi ('22) found the intima to be a glassy-like cuticular 

 layer most conspicuously present in the anterior region where 

 it has a thickness twice that in the other parts of the gland. 

 This structure appears to be hyalin in nature, reacting to stains 

 very similarly to sericin but more intensely in the anterior portion 

 of the middle region, this structure is not homogeneous but gives 

 the appearance of containing concentric bands whereby it is 

 possible to distinguish two or three layers of intima. This 

 arrangement in layers disappears anteriorly. 



