OSMETERIA OF PAPILIO LARVAE 377 



bicarbonate, and colors blue litmus paper red. It also appears from 

 the researches of Latter that these creatures in the imago state 

 secrete free potassium hydroxid, a substance for the first time known 

 to exist in the animal kingdom. 



In the caterpillar of Astyanax archippus (Limenitis disippus) a 

 dark, bladder-like sac is everted, but the lateral tubes appear to 

 be wanting, and no spray is sent out ; it occurs in the larvae of 

 many Nymphalidae and other butterflies and moths. 



These glands are functionally active in Perophora, but obsolete (at 

 least the external openings) in Lacosoma. 



The osmeterium in Papilio larvae. The caterpillars of the swallow- 

 tailed butterflies (Papilio, Doritis, and Thais), as is well known, when 

 irritated thrust out from a transverse slit on the upper part of the pro- 

 thoracic segment a large orange-yellow V-shaped fleshy tubular pro- 

 cess (the osmeterium), from which is diffused a more or less melon- 

 like but disagreeable, in some cases insufferable, odor ; the secretion 

 is acid and reddens litmus paper. The mechanism has been de- 

 scribed and figured by Klemensiewicz. 



When at rest, or retracted, the osmeterium lies in the upper part 

 of the body in the three thoracic segments, and is crossed obliquely 

 by several muscular bandies attached to the walls of the body, and 

 bv the action of these muscles the evagination of the osmeterium is 



i> 



strongly promoted. After eversion the tubes are slowly retracted 

 by two slender muscles inserted at the end of each fork or tube, and 

 arising from the sides of the 3d segment behind the head, crossing 

 each other in the median line (Fig. 366, i r.m.}. The secretion is 

 formed by an oval mass of glandular cells at the base of the forks ; 

 in the glandular mass is a furrow-like depression about which the 

 secretory cells are grouped. The secretion collects in very fine drops 

 on the side of each furrow opposite the glandular cells. 



According to C. D. Ash the larva of an Australian Notodontid 

 (Danima banJcsii Lewin) protrudes from the under side of the pro- 

 thoracic segment a Y-shaped red organ like that of Papilio ; no fluid 

 or odor is given out. 



Dorsal and lateral eversible metameric sacs in other larvae. The 

 showy caterpillars of Orgyia and its allies have a conspicuous coral- 

 red tubercle on the back of the 6th and also the 7th abdominal seg- 

 ment, which on irritation are elongated, the end of the tubercles 

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

 eversion the end becomes rounded and conical. These osmeteria 

 are everted by blood pressure, and retracted by a muscle. Fig. 366, 9, 

 represents a section of an osmeterium of Orgyia leucostigma when 



