No. 446.] 



PHOTINUS MARGINELLUS. 



cylinder, and follows the course of each tracheal branch, in 

 some cases almost to the main stem, so that instead of a struc- 

 ture resembling a cluster of grapes, one finds along the wall of 

 the cylinder a series of fan-shaped masses, one for each tracheal 

 twig, their apices toward the axis of the cylinder. (Fig. 8.) 

 As there is great irregularity in the form of these dark bodies 

 within the cylinder, and also in the shape of the intervening 

 clear spaces, it would seem that Emery is correct in considering 

 them an artifact. 



Definite cellular structure can be seen only in the material 

 fixed in Hermann's and Flemming's fluids. In these prepara- 

 tions, as in those from osmic acid, the tissue seems to be 

 shrunken and distorted. To a large extent the nuclei appear 

 to have been separated from the cytoplasm, and to lie in the 

 spaces left by the shrinkage of the cells. The cells show a 

 tendency to shrink away from each other, and away from the 

 main a.xis of the trachea, thus becoming smaller, denser bodies 

 surrounding the distal ends of the tracheal branches, and in 

 contact with the periphery of the cylinder. (Figs. 9 & 10.) 



In material fixed in alcohol or Gilson's fluid there is no appear- 

 ance of cells within the cylinder, although an abundance of small 

 nuclei may be clearly seen. 



Emery suggests that the cylinder, in Luciola, may be a syn- 

 cytium, but in both longitudinal and 

 transverse sections of the cylinders 

 in material of Photinus fixed in 

 Hermann's fluid, the cells are 

 clearly demonstrated. 



The "end-cells" of Lampyris 

 and the cylinders of Luciola are 

 stated to be a special development 

 of the tracheal epithelium. This 

 is not true of the cylinders in 

 Photinus, as the epitheUum can be 

 definitely seen, not only in the tra- 

 cheal axis, but even in the small branches. (Fig. 1 1 ) The epi- 

 thelium of the trachece of the photogenic tissue is altogether dif- 

 ferent from that figured by Wielowiejski for Lampyris. Instead 



