1914.] NATURAL SCIENCES OF PHILADELPHIA. 547 



till the majority of them lie posterior to the heavj' vein. In fig. 

 9, a, a row of them has broken loose from the hypodermal layer and 

 they are assuming the ovoid shape. At fig. 9, b, they are a little 

 farther advanced. In the 16-day-old stage the gland cells (fig. 10, 

 QIC) are much larger and lie just back of the heavy vein (fig. 10, v). 

 Now the chitinous tubes (fig. 10, Tu) are formed and they are con- 

 nected with the gland cells. 



3. Origin of Chitinous Tubes. 



In the 15-day-old stage may occasionally be seen hypodermal 

 cells having processes. Such cells lie at the place where the chitinous 

 tubes later appear. One of these cells (fig. 11a) has a large and 

 conspicuous nucleus. The growing point of the process appears to 

 have no cell wall. Twelve hours later the hypodermal cells (fig. 116) 

 forming the tubes have become much smaller, no doubt because of 

 the formation of long processes. It seems that the more the processes 

 grow in length, the more the cells diminish in size. Each hypodermal 

 cell, therefore, must serve as a storehouse for building a tube. When 

 the process is far advanced, its cytoplasm probably begins secreting 

 a substance which in a short time is transformed into the chitinous 

 tube. In fig. 116 the tube is developed and it is connected with the 

 exterior, but the cytoplasm surrounding the tube has not yet dis- 

 appeared. In a little later stage (fig. lie), the cytoplasm surrounding 

 the tube has all disappeared except a small process of the cell. The 

 tube is now connected with a gland cell. 



4. Development of Gland Cells. 



As already stated, the gland cells were originally hypodermal 

 cells (fig. 9, a and 6) which migrated from the hypodermal layer. 

 This migration occurs in worker pupse 15 days old. In 16-day-old 

 worker pupse these cells (fig. 10, GIC) are three or four times as large 

 as they are in the 15-day-old stage and they begin to resemble true 

 gland cells. In the 17-day-old stage they are still larger (fig. 12, 

 GIC). Their nuclei are extremely large and stain less densely than 

 does the cytoplasm with Ehrlich's hamatoxylin and eosin. By the 

 ninteenth day the gland cells (fig. 13, GIC) have enlarged but little 

 since the 17-day-old stage. In 21-day-old worker pupse (age at which 

 they emerge from their cells) the gland cells (fig. 14, GIC) seem to be 

 perfectly developed in all respects, except they are only about two- 

 thirds the size of the gland cells (fig. 15, GIC) in old worker bees. 

 36 



