344 



TEXT-BOOK OF ENTOMOLOGY 



numerous, may combine among themselves, so that the spinneret 

 is susceptible of assuming during the process of spinning still more 

 diverse positions. 



FIG. 337. Portion of the silk-gland of Boinbya? mori : j>, tunica propria ; i, tunica intima; 

 , secretion -cell with branched nuclei ; ft, separate secretion-cell from the anterior part of the silk- 

 gland of AmjtfiitliiKix betularia ; b, the same of Vane ana urticcB ; a, the same in Smerinthus 

 tilice. After Helm. 



Histologically the silk-glands are composed of three layers, the 

 outer, or tunica propria (Fig 337) ; the inner, the tunica intima; the 



Fro. 338. A, section of gland of lepldopter : B, section of silk-gland of a saw-fly larva; n, nu- 

 cleus ; i.d, canals ; </..v, cavity. After Gilson. 



middle layer being composed of extraordinarily large epithelial cells 

 which can be seen with the naked eye, and are also remarkable for 

 the branched shape of the nuclei (a, b, c, 337), the branches being 



