No. 504] ORIGIN OF FROTH IN SPITTLE-INSECTS 791 



They are granular and occupy a large portion of the cell. 

 The protoplasm in the region of the nuclei is highly gran- 

 ular and is readily stained. In the periphery of the cell 

 it is not stained as readily, appearing somewhat hyaline. 

 In some of the preparations made with specimens which 

 had been killed in alcohol there were a number of inter- 

 cellular spaces, while in the preparation of the glands 

 which had been fixed immediately after removal of the 

 fatty tissues such appearance was lacking, except in 

 places where it was obviously due to mechanical cause. 

 Arnhart (1906) gives a photomicrograph of a surface 

 view of the wax-glands of bees, and explains these open- 

 ings as tracheal in nature. Their presence is, in my 

 opinion, due solely to faulty preparations rather than to 

 the presence of any special tracheal ramifications. In 

 general appearance the cells in surface view are very 

 similar to those of the wax-glands of the honey-bee. A 

 comparison with the excellent figures of Dreyling (1905) 

 serves to bring this out clearly. 



In longitudinal sections of A. parallela and Lepyronia 

 quadrangularis the hypodermal cells of this region are 

 greatly enlarged (Fig. 5), and strikingly resemble those 



of the wax-gland of the bees. Each gland has the appear- 

 ance of a curved band or bow, the central portion of which 

 is thick, while it gradually tapers towards the ends. The 

 same thing is noticed in the cross section (Fig. 6). This 

 appearance is due to the general decrease in height of the 



