APRIL,' 1906. THE CHEMICAL NATURE OF SOME INSECT SECRETIONS. 33 



color seems to be produced not by indol, however, but rather by 

 the burnt chitin or animal fat, as other insects which did not have 

 an indoloid odor gave the same result. The very delicate and 

 characteristic test with strong hydrochloric acid and a pine 

 splinter was also tried, but with negative results, as no red or 

 purple color was developed. As it is not an indol and yet has a 

 fecal odor it would seem that it must contain a leucin. Its solu- 

 bility also indicates the presence of this substance since it is 

 readily extracted from the ants by water or ether, but not at all 

 by absolute alcohol. When an ethereal extraction of the ants is 

 rapidly evaporated under reduced pressure a few pearly fat 

 globules are obtained, which are in part soluble in water, while the 

 addition of alcohol causes a globule to separate for a few moments 

 (leucin and fat?), later to disappear. After evaporation of the 

 alcohol from this and freezing the residue, some crystals very 

 much resembling leucin could be observed under the microscope, 

 although contaminated greatly and rendered somewhat obscure 

 by the large amount of fat present in the mixture. These crystals 

 w^ere very distinct w^hen the flask was cold, but as it became 

 warmed up to the room temperature they melted or dissolved 

 in the fat. 



The original ether extraction is neither acid nor alkaline to 

 indicators, and on saponification with potassium hydroxide gives 

 no odor of amonia. but a smell resembling oenanthol, which most 

 probably arises from the fat and not from the odorous principle. 

 Thus although there is no positive evidence that the substance 

 present in Eciton is actually leucin, nothing seems to oppose such 

 a conclusion. 



That the Eciton odor has considerable biological significance 

 is very probable. These ants are totally blind, and migratory in 

 their habits, so that they must depend almost entirely upon a 

 sense of smell to follow one another about. Thus it can easily 

 be seen how much a strong odor might be developed through the 

 action of natural selection, from the small trace of leucin that is 

 usually present in insect feces. (Concerning the normal pres- 

 ence of leucin in the alimentary tract of insects see Plateau {'72,)-) 



II. FORELIUS FCETIDUS. 



The Texan species of this monotypical genus, like the species 

 of Tapinoma and a few other closely related ants, has a very 

 strong and peculiar odor which has been very aptly described by 

 Buckley ('66), and later by Forel, as closely resembling "rotten 

 cocoanuts." 



