144 AMERICAN NATURALIST. [Vol. XXXVIII. 



clearness in all the osmic acid material, and in one insect fixed 

 in Flemming's fluid. In the typical osmic acid preparation they 

 appear as irregularly spherical bodies, blackened throughout but 

 most intensely so at the point of origin of the tracheoles. They 

 show no appearance of nuclei, but as the nuclei of the adjacent 

 cells show only faintly with this treatment, this is not significant. 



The transition cells of Photinus as shown in osmic acid 

 preparations are more similar to the blackened, grape-like bodies 

 described by Emery, than to the stellate, endothelioid cells 

 figured by Wielowiejski. They occur at the apices of the finer 



tracheal twigs, and near the periphery of the cylinder. The 

 space between them and the tracheal axis, and the spaces 

 between the transition cells themselves appear clear. The edges 

 of the spheroid masses are generally irregular, and their whole 

 appearance suggests an artificial condition. (Fig. 7.) In sec- 

 tions where the effect of the osmic acid has not been as exten- 

 sive, the same blackening at the points of tracheolar origin may 

 be seen, but instead of finding spherical bodies surrounding these 

 points of furcation, the granular mass of the cylinder appears in 

 different condition. It extends along the periphery of the 



