1914.] NATURAL SCIENCES OF PHILADELPHIA. 555 



Fig. 8. — Cross section of a small portion of posterior part (PoslP) of membrane 

 from fig. 2 at /, after treatment with caustic potash, showing that tubes 

 {Tu) are chitinous. 



Plate XX. — Fig. 9. — Sagittal section through articular membrane of a 15-day- 



old worker pupa (counting from tlie time the egg was laid), showing origin 



of gland cells from hypodermal cells (HypC). All material used for figs. 



9 to 166 was fixed and stained. 



Fig. 10. — Same kind of section as fig. 9, from a 16-day-old worker pupa, showing 



(1) great increase in size of gland cells (GIC) within one day's time; (2) 

 presence of tubes (Tu); (3) thin hypodermis {Hyp); and (4) presence of 

 chitin {Ch). 



Fig. llfl-c. — Origin of chitinous tube from a hypodermal cell. 11a is from a 

 15-day-old worker pupa, and life and lie are from a 15|-day-old worker 

 pupa. 



Fig. 12. — Same kind of section as fig. 9, from a 17-day-old worker pupa, 

 showing, as compared with fig. 10, (1) a slight increase in size of gland cells; 



(2) a thinner hypodermis; and (3) thicker chitin. 



Fig. 13. — Same as fig. 12, but from a 19-day-old worker pupa, showing no 



noticeable change in size of gland cells. 

 Fig. 14. — Same as figs. 12 and 13, but from a 21-day-old worker pupa (now 



emerged as an imago insect), showing; (1) a considerable increase in size 



of gland cells, and (2) thicker chitin. 

 Fig. 15. — Same as fig. 14, but from an old worker bee, showing a still greater 



increase in size of gland cells. Compare this large gland cell, which was 



fixed and stained, with the large live gland cell in fig. 5. 

 Fig. 16a. — Large gland cell from an old queen. 

 Fig. 166. — Large gland cell from a middle-aged pupal queen. Compare 



fig. 16a with gland cell in fig. 15. 



