FILIPPFS GLANDS 



345 



more or less lobed, and the larger the cells the more numerous are the 

 branches of the nucleus. Gilson 1 finds that those of Trichoptera, 

 Lepidoptera, Diptera, and Hymenoptera ordinarily consist of a 

 small number of cells; and it is 

 quite common, he says, to find only 

 two cells in a transverse section 

 (Fig. 338, A). In the Tenthredi- 

 nidae, however, " the organ still con- 

 sists of a tube, the wall of which is 

 composed of flat cells, but in addi- 

 tion to that, two series of spheroidal 

 cells are attached to the sides. Each 



P , , -i, , ,. FIG. 339. Branching nucleus of spinning 



OI these Cells Contains a System Of gland of Pleris larva. After Korschelt, from 



tiny canals running through their 



cytoplasm (B, i. d). These cells are the secreting elements; they 

 continually cast the silk substance into the tube." A peculiarity 

 of the tunica intima is its distinct transverse striation. 



The lining of the 

 glands and of their com- 

 mon duct is moulted 

 when the caterpillar 

 casts its skin, arid this, 

 as well as the mode of 

 development, shows that 

 the glands are invagina- 

 tions of the ectoderm. 

 Gilson finds that the 

 silk - glands and silk- 

 apparatus of Trichoptera 

 are very similar to those 

 of caterpillars, and that 

 the silk is formed in the 

 same way. 



Appendages of the silk- 

 gland (Filippi's glands). 



FIG. 340. -Filippi's glands (ff) isolated and seen from I n mos t larvae there 



above : e, e, its lobules ; d, its excretory canal ; E, silk-duct ; 



(7, common canal; c, upper spinning muscle; b, lower mus- jg either a single Ol' a 



cle ; a, lateral muscle ; T, spinneret. After Blanc. 



pair of secondary glands 



which open into the spinning glands near their anterior end. They 

 are outgrowths of the gland provided with peculiarly modified excre- 



1 On cytological differences in homologous organs. Report 63d meeting of British 

 Assoc. Adv. Sc. for 1893. 1894. p. 913. 



