382 



HISTOLOGY 



basement membrane 

 is homogeneous and 



A transverse section of this tubular gland shows the following main 

 layers. A single outer layer of large muscle fibers which extend the 



length of the gland and are 

 consequently seen in transec- 

 tion. The sections are roughly 

 square or triangular owing to 

 the compact way in which the 

 fibers are arranged in the 

 layer. The illustration (Fig. 

 348) shows three of these 

 structures. Their myo-fibrils 

 are placed in radiating plates 

 or muscle columns, and the 

 free sarcoplasm is collected in 

 the center where the nuclei are 

 also most frequently found. 



The next layer is formed 

 by a 

 which 



much thicker than such struc- 

 tures usually are. The poison 

 epithelium is probably the ac- 

 tive agent in its formation. 



Inside of the basement 

 membrane is found the poison- 

 secreting epithelium. This 

 layer is composed of a single 

 layer of very high, narrow cells 

 whose lateral boundaries are 

 difficult to see. The nuclei are 

 large and placed well up from 

 FIG. 348. -Section of the wail of the poison gland of the basement membrane, al- 



a spider, Lycosa speciosum, seen in cross section. . , . 



mus., three muscle cells; b.m., basement mem- though they are irregular in 



brane; p.n., poison-cell nuclei; p.gl. globules of t h at respect and SOniC of them 

 poison, x 580. x .mi i 



rest close to it. These nuclei 



have a peculiar chromatin pattern which close study might enable one 

 to specifically identify from the other nuclei of the animal. The cyto- 

 plasm is most markedly striated by fibrillar structures, which reach 

 from the basement membrane to the distal edge of the cell. In fact 

 they reach beyond this edge, and so obscure it that it cannot be definitely 

 determined. Outside of the cells these fibrils end in a loose reticulum 

 which fills the lumen and contains the poisonous fluid in its meshes. 

 The poison appears as a few yellow, scattered droplets in the outer 



