94 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 



tinuation of the intima lining the epithelium of the reservoir and 

 extending over the mouth of the glandular cell, reaching down into 

 the interior to the vacuole. Surrounding this little canal there are 

 two guard cells which are distinguishable by their nuclei (N^). It 

 is possible that the function of the guard cell is to secrete the chitin 

 lining the little canal. 



The vacuolated condition of the cytoplasm in Figs. 9-10 is prob- 

 ably due to the fact that the fixer has dissolved out the secreted 

 fluid which fills these vacuoles, leaving only the large granules 

 (Gr.) , while in Fig. 1 1 the fluid has been coagulated by Flemming's 

 solution. 



Owing to lack of time, it has been necessary to omit the study of 

 the gland in the pupa. Claus states that the reservoir is retained 

 in the larval skin, in which the lower portion of the pupal body is 

 enclosed. According to him, the pupa is still able to discharge 

 droplets of the secretion by wriggling vigorously when disturbed. 

 This point demands further investigation. 



The size of the glandular cells varies between 75 and 87 mm. 

 Claus gives their number in AleJasoma [L/;?rt] populi as thirty to 

 forty-five for the thoracic and twelve to twenty for the abdominal 

 glands. In Melasnma lappnuica, on the other hand, I have found 

 only fifteen in the thoracic glands and seven in the abdominal ones. 



The size of a thoracic gland in its retracted state is about 0.75 

 mm. in its longest axis, including the glandular cells, and about 0.30 

 mm. at its base. The abdominal glands are about two-thirds the 

 size of the thoracic ones. 



As to the chemical composition of the secretion, no attempt was 

 made to establish anything beyond the fact that it is acid reacting. 

 Neither was there any attempt to work out the nerve supply. 



In conclusion, I wish to express here my sincerest gratitude to 

 Professor William A. Riley, under whose supervision this has been 

 worked out, for his kind encouragement and instructive criticism, 

 without which this work would have been impossible. 



