ADHESION AND SPINNING 



the section in transverse section, showing its surrounding covering of 

 cells with a nucleus belonging to one of them. As may be seen in 

 the figure the lines of demarcation of the cells are obscure or, in 

 places, not perceivable. A marked peculiarity of all of them, in the 

 insects, is the great branching of the single nucleus in each cell. The 

 figure shows three sections of these branches, two of which belong to a 

 single nucleus. The chromatin is finely granular, and a plasmosome 

 does not appear in the section. 



The cytoplasm is granular, and some of the granules are arranged 

 in larger bodies much as they are in nerve-cells. These masses have 

 an apparent axis which shows a tendency to lie parallel with the main 

 axis of the cell. They are also larger in the proximal part of the cell 

 and diminish in size towards the distal part. The distal surface of the 

 cell, where it borders on the lumen, is coarsely but weakly striated. The 

 nuclei of these cells should be examined in a freshly dissected gland from 

 a cabbage worm (Pieris) to observe their peculiar shape. 



The silk lies in the lumen as a thick fluid or semi-fluid mass. It is 

 seen to have a peripheral layer of lighter material which may possibly 

 be the fluid that is used to attach the main thread by, or may be a stage 

 in the elaboration of the silk. The secreted material is used by forcing 

 out a compressed end of this mass and passing it through the spinneret. 

 It is used not only to build a protecting cocoon, but also to assist the 

 animal to adhere and progress (in many ways). 



Technic. All these tissues cut fairly well with ordinary fixation 

 and paraffin sectioning. It is always important to keep the secretion 

 in situ, and to embed and cut so carefully that it does not fall out of the 

 sections or shrink so as to distort the pictures produced. The combined 

 paraffin and celloidin process is of use when the material is fragile ; and 

 when it is tough and refractory the celloidin process alone is of most use. 

 In staining, it is well to use some stain that will differentiate the secretion 

 material strongly. Most stains do this more or less, but some of the 

 diffuse analine dyes, as cosine, are particularly favorable. With such 

 stains the finer strands of the material can be traced to the cells which 

 produced them. 



LITERATURE 



SCHNEIDER, K. C. "Lehrbuch der Histologie," S. 282, 1902. 



BOURNE, G. C. "On the Structure of ^Enigma <znigmalica," Quart. Journ. Mic. Sc. N. S., 



No. 202 (Vol. LI, Part II), 1907. See p. 282 on byssus gland. 

 GILSON, G. "Recherches sur les cellules secretantes," "La soie et les appareils serici- 



genes, I, Lepidoptera," La cellule, 1890, p. 115. "II, Trichopteres," La cellule, 



1893, p. 71. 



2E 



