ELEMENTARY BIOLOGY. [CHAP. 



(commissures}. Lying in the sternal canal be- 

 neath the ganglia may be seen the sternal 

 artery (15). 



S. Follow back the single cord proceeding from 

 the last thoracic ganglion to the abdomen, 

 removing any muscles which come in the way : 

 it will lead to a chain of six ganglia, one for 

 each abdominal segment, united by single 

 cords. 



17. The green gland. A soft greenish mass lying on 

 each side in the extreme front part of the cephalo- 

 thoracic cavity: pass a fine bristle into it from the 

 opening of its duct on the basal joint of the endo- 

 podite of the antenna (21. f.). 



1 8. Tease out a bit of muscle in water and examine 

 it microscopically: note its structure; it is made up 

 of fibres, marked by regularly alternating transverse 

 lighter and darker bands. 



19. Tease out a bit of perfectly fresh nerve-cord in water 

 and stain with magenta or riDematoxylin. 



a. Composed of slender fibres of varying size, each 

 consisting of a structureless outer wall, on which 

 are nuclei at intervals, surrounding a clear or, 

 sometimes, finely granular or obscurely fibrillated 

 central axis. 



20. Tease out in water a ganglion which has been treated 

 with osmic acid. 



a. Composed of large oval branched cells, each con- 

 sisting of a granular mass in which lies a clear 

 round nucleus, containing a nucleolus. 



