No. 504] ORIGIN OF FROTH IN SPITTLE-INSECTS 



793 



of the gland, while in the margin the measurements are 

 approximately 16 by 14 microns. The nuclei are round 

 or oval and are situated in the lower margin of the cell. 

 They are very granular and stain deeply. They are 

 about 8 by 6 microns in dimensions. The protoplasm 

 is highly granular, much more so in the region of the 

 nuclei and in the margin underneath the chitin. The 

 cuticula over the gland is about 8 microns thick, while 

 that of the adjacent body wall is 12 microns. 



If one makes satisfactory sections through the glands 

 of these insects it is very easy to see extremely minute 

 openings in the overlying cuticula leading from the 

 glands to the surface. These outer openings correspond 

 to those described above. For each canal there is a pore. 

 Their distribution over the gland is regular. They are 

 unbranched, perpendicular to the surface of the cells and 

 about equally distant from one another (Fig. 7). As has 



been stated, similar pores do not occur in other regions 

 of the body wall. Berlese (1907) and many other writers 

 hold the opinion that true pores are never present in the 

 chitin, and that substances are not conducted through the 

 chitin by any such arrangement. Dreyling (1905), in a 

 paper already referred to, figures and describes canals in 

 the chitin overlying the wax cells of the social bees, and 

 ascribes to these the function of conveying wax to the 

 outer surface. Many writers agree with Dreyling in this 

 view. My studies of the cuticula in the spittle insect 

 convinces me that such true pores are present and they 

 do serve as conduits in carrying the secretions of the 

 underlying glands to the surface. It was noticed on 

 several occasions that in specimens dropped in hot Flem- 



