﻿Sept. 1S95.] Packard. Scent Glands of Insects. 121 



{Danima banksii Lewin) protrudes from the under side of the prothor- 

 acic segment a y-shaped red organ like that of Papilio ; no fluid or odor 

 is given out. 



The showy caterpillars of Orgyia and its allies have a conspicuous 

 coral-red tubercle on the back of the sixth and also the seventh abdom- 

 inal segment, which on irritation are elongated, the end of the tubercles 

 being eversible. When at rest the summit is crateriform, but on ever- 

 sion the end becomes rounded and conical. These osmeteria are everted 

 by blood pressure, and retracted by a muscle. Plate V, Fig. 9 repre- 

 sents a section of an osmeterium of Orgyia leucostigma when retracted 

 by the muscle (w); at the bottom of the crater are the secreting or gland- 

 ular cells {gc), being modified hypodermal cells. These doubtless serve 

 as terrifying organs to ichneumons and other insect enemies, and though 

 we have been unable to detect any odor emanating from the tubercles, 

 yet doubtless they give out a scent perceived by and disagreeable to 

 their insect assailants. 



In the HemileucidK there are two pairs of lateral osmeteria, which, 

 however, are not highly colored (PI. V, Fig. 10). In Megalopyge {Lagoa) 

 there is a lateral row of singular pale permanently everted processes 

 which appear to be the homologues of the osmeteria of larvse of other 

 lepidopterous families. 



In the caterpillars of certain blue butterfles (Lycjenidae) is an in- 

 ternal osmeterium, being a very minute sac which is everted from a 

 transverse slit on the top of the seventh abdominal segment. Its func- 

 tion is quite the opposite of those of the caterpillars of other families 

 since the sac exudes a sweet fluid very attractive to ants, which may be 

 diffused more widely by the delicate spinulose bristles crowning the 

 summit. W. H. Edwards states that in several species of Lyccena, be- 

 sides that on the seventh abdominal segment, there is on the eighth seg- 

 ment a pair of minute dorsal evaginable tubercles. 



In certain of the butterflies, the He/icouida: {Colcenis, Heliconiiis, 

 Euides and Dione), there is thrust from the end of the abdomen a 

 pair of large irregular rounded evertible glands, which give out a dis- 

 agreeable odor, and are consequently repellant, and which seem to be 

 the homologues of the odoriferous glands of other butterflies. 



The large soft rounded evertible glands, looking like puff-balls or 

 a rounded pudding (PL V, Fig. 12) are everted, when the butterflies are 

 roughly seized, from the dorsal side of the penultimate segment of the 

 abdomen. The males possess two smaller tubercles on the inside of the 

 anal claspers or lobes. Miiller also detected, in the females of vari- 



