No. 533] PHOTOGENIC ORGANS OF LAMPYRIDJ2 309 



interior as far as the point where they enter the reflect- 

 ing layer; the presence of these hairs in trachea 1 beyond 

 this point and in the fine tracheoles. lias not been ob- 

 served. In their passage through the photogenic tissue, 

 the trachea 1 are surrounded by the structure referred to 

 by Miss Townsend as the cylinder, a cylindrical mass of 

 ••ells, sharply differentiated from those of the surround- 



•»g tissue, through which the trachea passes almost cen- 

 trally. Within this cylinder the trachea throws off the 

 numerous small branches, which at the edge of the cyl- 

 inder break into the very fine tracheoles which pass into 

 the photogenic tissue and anastomose between the cells 

 with tracheoles from adjoining cylinders. The appear- 

 ance of the large tracheae above the luminous organ are 

 shown in Fig. 2, drawn from an oblique section, the line 

 of the cut being nearly parallel to the line of the larger 

 trachea? near the edge of the abdomen. At the lower end, 

 just next to the superficial chitin covering the luminous 

 segments, the main trachea subdivide into the large num- 

 ber of branches whose tracheoles radiate into the photo- 

 genic tissue, usually recurving slightly, so as to penetrate 

 the tissue a short distance from the chitin. 



The entire system suggests that the air is drawn in 

 through the breathing trachea?, and forced through the 



