7 6 



ENTOMOLOGY 



duct, which passes through the tubular spinneret. Two divisions of 

 the spinning tube are distinguished: (i) a posterior muscular portion, or 

 thread-press and (2) an anterior directing tube. The thread-press com- 

 bines the two streams of silk fluid into one, determines the form of the 

 silken thread and arrests the emission of the thread at times, besides 

 having other functions. The silk fluid hardens rapidly upon exposure 



to the air; about fifty per cent, of the fluid 

 is actual silk substance and the remainder 

 consists of protoplasm and gum, with traces 

 f of wax, pigment, fat and resin. 



FIG. 106. Silk glands of the 

 silk worm, Bombyx mori. cd, 

 common duct; d, one of the 

 paired ducts; g, g, Filippi's 

 glands; gl, gland proper; p, 

 thread press; r, reservoir. 



FIG. 107. Sections of silk gland of the silk worm. 

 A, radial; B, transverse, b, basement membrane; *, 

 intima; 5, glandular cell with branched nucleus. 

 After HELM. 



A transverse or radial section of a silk gland shows a layer of glandu- 

 lar epithelial cells, with the usual intima and basement membrane (Fig. 

 107) ; the cells are remarkably large and their nuclei are often branched; 

 the intima is distinctly striated, from the presence of pore-canals. The 

 glands arise as evaginations of the pharynx (ectodermal) and the chi- 

 tinous intima of each gland is cast at each moult, along with the general 

 integument. 



