1919] Repiignatorial Glands 47 



Since the direction of the spray appeared to correspond to 

 the direction in which the head was free to move we obtained a 

 fresh larva and held the head so that there was practically no 

 movement to the right or left. In response to stimulus under 

 these conditions the larva was still able to throw a spray of 

 the liquid to the distance of from 6 to 7 inches, but wholly in a 

 posterior direction over the entire body. This experiment was 

 repeated with another larva with similar results. It appears 

 evident that the caterpillar can direct the liquid backward to a 

 distance of several inches even though the head be prevented 

 from free movement to the right or left. Moreover, experiments 

 show that the larva can project the spray in an anterior direction. 



The caterpillars under observation were too far advanced to 

 determine whether the larvae possess functional glands in all of 

 the earlier instars. A late brood, however, was found in which 

 the larvae were in the next to the last instar. One of these 

 larvae, after what seemed to be a greater degree of irritation 

 than usual, did eject a considerable quantity of the fluid, the 

 farthest drop falling at a distance from the body of about 33^ 

 inches. We hope to be able, next season, to make further 

 investigations of this phase of the subject. 



The opening of the gland is a narrow transverse slit on the 

 ventral side of the prothorax close to the cephalic border of 

 this segment.. The gland is sack-shaped and situated within 

 the thoracic cavity. It appears to be quite similar to the 

 corresponding gland in Cerura vinula described by Klemen- 

 siewicz.* Further detailed description of this gland and its 

 morphology will be presented by the Junior author in a later 

 paper. 



Regarding the chemical nature of the secretion it is sufficient 

 to say here that it gives a marked acid reaction with blue litmus 

 paper and that it has a pungent and characteristic odor that 

 immediately suggests acetic acid. The subject is under careful 

 investigation in conjunction with Professor E. M. Chamot of 

 the chemical department, the results of which will be given in a 

 later paper. Suffice it to say, the investigations indicate tha:t 

 the secretion is formic acid. Poultonf has already shown that 

 the secretions from the similar gland in Cerura vinula is formic 



* Verhandlungen d. Zool. Bot. Gesellsch in Wien. Vol. 32, pp. 468-474, 1882. 

 t Trans. Lon. Ent., Soc. for 1886, p. 157. 



