194 N. E. McINDOO 



it becomes a tube with thick walls at first, but the walls gradually 

 become thinner and thinner as one glances at them from the proxi- 

 mal end to the distal end. The outer layer of the walls seems 

 solid, often does not take the stain, but remains a Hght yellow 

 color. The inner layer does not appear totally solid, but usually 

 is stained more or less. The axial tube seems harder than the 

 surrounding tissue and occasiona-Uy the microtome knife fails 

 to cut it, thus leaving it slightly projecting from a cross-section. 

 Hence from all appearances the axial tube is a semichitinous 

 structure. 



The head end of the axial tube terminates in the cone (fig. 20, 

 Con), from the center of which arises the short axial fiber (AF), 

 scarcely visible under the highest magnification. In position 

 this fiber corresponds to the Schon's axial fiber, which extends 

 the full length of the enveloping cell. Figure 24 shows the rela- 

 tion of the various parts in cross-section just in front of the cone. 

 The dot represents the axial fiber; the inner circle, the walls of 

 the axial tube; the middle circle, the walls of the enveloping cell, 

 and the outer circle, the walls of the cap cell. 



The cytoplasm in the distal half of the enveloping cell and in 

 the cap cell (fig. 20, CC) appears sHghtly net-hke, although this 

 appearance is exaggerated in figures 20, 23, and 24. 



In regard to the development of the chordotonal organ, Schon 

 says that eight days after the honey-bee egg is laid a small growth 

 projecting into the blood chamber is seen developing in the 

 hypodermal cells in the tibia from which the organ arises. On 

 the ninth day may be seen the first differentiation of cells, and 

 on the tenth and eleventh days one may distinctly see sense cells, 

 enveloping cells, and cap cells. On the eleventh and twelfth days 

 the cone is formed, and on the thirteenth day the nervous part 

 of the organ is laid down in the blood chamber. On the fifteenth 

 and sixteenth days the end fibers are developed, and on the 

 seventeenth day the organ is fully developed. It is of a purely 

 ectodermal formation. 



Schon says that since the trachea is so greatly expanded where 

 the chordotonal organ occurs, it may probably have something 

 to do with the function of this organ; but the present writer does 



