No. 489] SILK (U.AXDS OF M'.WTFJ.ES 



575 



tion of how the thread is first forced to the exterior and also how it 

 is extruded when broken. 



It is not necessary for us to describe the mechanism of spinnini; 

 as that has been fully done by Blanc and Gilson for the Lepidop- 

 tera and their descriptions serve equally well for the liv-UKMioptcrous 

 larvae. The method of spinning the cocoon in A panfrh.s filnimm- 

 tus has been well described and figured by Reaumur. 



The Spinneret.— From the i)ress a sliort chitiuous tube leads to 

 the .spinneret .^p. Fig.. lN. 2\) and :5(> . The lunu'ii of this tube 

 gradually widens as it a|)pr()aches the ('xierior Kiu'^. L*!i and 'AO). 



press occupies .4 mm. The spinneret is situated just beneath the 

 buccal cavity and consists of two small chitinous projections 

 directed cephalo-dorsad (Fig. 28, sp.). 



Functions of the Different Parts of the Silk Gl&nd.—Ahdotm'nal 

 Dirision. A. previously pointed out the abdominal division of 

 the silk glands consists, i'n the young larva(^of tN\o pairs <,f straight 

 cylindrical tubes lyinu' on each si.le of tin- alinientaiy eanal. As 

 the larvae urow these parts beconie active, their hiniina become 

 gradually di<tend(>il with the s(>ert>ted i>roduet till, in the mature 

 forms, the ulanduiar walls are so thin as to warrant the assertion 

 that tlieyhaNepraetieally ceased to sccivte and are nicrelv rcscrxoirs 

 for the accumulated product. 



'Fhe (|uestion as to whether the "gres" <.r - ^^luu" is scvreted 

 by one j.artieular reo-ion of the gland and the silk by another is still 

 unsettled, (iilson in 1S!»0 and auain in l v.»4 came to th(> conclu- 

 sion that both are secreted throughout the gland; and that the 

 silk, properly speaking, is the result of a selection etl'ected in rhe 

 layer of secreted pn.duct lyin- next the internal fa<'e of tin- cells. 

 AVhether this proccs. ,)f schn-tion is a ehemi<-al phenomenon or 



a sru.ly o'f -'everai series of sections he conclud'es that the outer or 



spe.-ial afHm-tv for colorinu' a-ents" Neither ..f Ihes.- conclusions is 

 absolute since he. lid nor (ind then, to hohl I nie in all eases. 

 Hlanc. •SI), p. L'[. stams that "The silk sc 



