90 JOURNAL. OF ENTOMOLOGY AND ZOOLOGY 



tubercles only a few seconds, olten even less than a second, and then 

 they were withdrawn, mostly (but not always) simultaneously anci 

 suddenly into the interior. The larva was capable of discharging its 

 odorous secretion five to six times in succession. An examination 

 of the bead-like droplet under the binocular microscope showed that 

 it was shiny, white, globose and constricted at the base. One larva, 

 from which the disturbing needle was not withdrawn for some time, 

 kept the droplets out for about six to seven seconds at a stretch until 

 some finally burst and the fiuid spread over the surface of the bociy. 

 It could plainly be seen that the broken membrane was quickly with- 

 drawn into the interior. x\fter a few seconds there was another 

 ciischarge, but this time the droplet was no longer globose nor white, 

 but more or less shapeless and yellowish at the bottom. The Huid 

 this time spread as soon as discharged, while the broken membrane 

 remained for two or three seconds in a shapeless mass on the out- 

 side, and was then withdrawn. This was repeated four to five 

 times until the larva was utterly exhausted. 



These observations indicated that below the tubercle there was 

 a reservoir full of the secretion, of which only a small portion was 

 discharged each time by eversing only a portion of the reservoir. 

 It was evident that the insect was very economical with its secretion, 

 keeping it out only long enough to ciiffuse the strong odor, although 

 it had evidently a larger supply of the fluid ready in storage. This 

 economical use of the secretion is mentioned by Claus. How the 

 insect is able thus to economize with the Huid will be e\'ident when 

 the anatomy of the gland is discussed. 



As to the function of the strong smelling secretion, it is e\'ident 

 that it is protective, from the fact that it is discharged only when 

 the larva is disturbed, and that it is not present in the adult. Its 

 odor in itself is a strong indication of its protective function. 



Anatomy and Function of Parts 



The general structure of the gland and its operation is shown in 

 Figs. 1 and 2, which are slightly diagrammatic. Figure 1 represents 

 the gland in its retracted position. As is shown, the gland consists 

 of a reservoir (R), which is an inpocketing of the cutaneous epithe- 



