20 ffl *— ^ M ^ Ml ^ Bf< w .^ m ii 



supporting; the glands so as to fix them in their positions. Tliey jx nett rate flee[) 

 into the bodies of the ghnnd-eells, piercing througli the Innica propria. In tlie first 

 step of this penetration, the propria, wliicli is higlily elastic, is not bored, as one 

 miglit presume, by the pushing force of the growing tips of trncheie ; but this 

 elastic lamella is dissolved, in points of contact with tlie tracheal tips, by some 

 enzyme substance secreted from the latter. The traclical tnbes which penetrated 

 the glands branch repeatedly, to be at last divided into finest capillaries, which 

 show no trace of tsenidia and are lost iji free termination within the cytoplasm ; in 

 this way, they become distributed everywhere in the cell-bodies. In spite of 

 my efforts, no traces of socalled "TracljeenkapiUareudnetz" by Wistinohausen '^ 

 have been observed. Every ecdysis is preceded by a formation of a new series of 

 tsenidia coming into view immediately beneath the peritoneal cells. Therefore, on 

 cross sections through the gland in this stage, the old tjcnidian ring is revealed 

 inside a new one. Furthermore not uufrequently, double rings of old ttonidia 

 surrounded with a new ring are seen. 



3) Contrarily to the obs'rvation by G. Joseph ''\ there is found no trace of 

 nerves standing in connection with the silk glands. The connective tissues and 

 tracheal tnbes, ramifications of whicli are in close resemblance to nerve fibres, are 

 probable to be mistaken for nerves. 



4) Tunica intima in the anterior division is a continuous layer provided with 

 fine radial striations. The spiral markings are observed, on the intima of the 

 middle division, by some previous authors ; bat their peculiar condition in tiie 

 posterior division is, so far as L am aware, yet noticed by none. The spiral 

 markings on the intima are regular in arrangement and run in parallel in the 

 middle division, and is gradually disturbed towards the lander part of the gland, 

 so that they are converted into a net-form markings. 



5) In the silken column contained in the gland-lumen are distinguishable two 

 distinct layers, the sericin and the fibroin. Views of previous authors concerning 

 the silk formation or the production of the sericin and fibroin are wid(>ly divergent 

 from one another. Bolley's view may be looked upon as having totally been 

 abandoned. Gilson's "selection" theory '^^ appears also to be hardly intelligible. The 



1). C. V. Wistinghausen : Tracheenendigungeu in den Sericterien der Eanpen. Zeihchr. f. wiss Znol 

 XLIX, 1S90. pp 565-582. 



2). G. Joseph: Vorläufige Mitteilung über Innervation und Entwickelung der Spinnors^ancn bei 

 Insekten. Zool. Anzeig. 1880. pp 326-328. 



3). G. Gilson : Eecherches sur les cellules secretantes. La soie et appareils serieioenes Ln cellule 

 1890, 1893. ' 



