76 SAMUEL H. SCUDDER. 



longing properly to the sub-costal, of which it is the only inferior 

 branch. 



The possession of the peculiar scent organ, however, is unquestion- 

 ably a mark of high development. Wallace writes :* " When we con- 

 sider this singular apparatus, which in some species is nearly half an 

 inch long, the arrangement of muscles for its protrusion"}" and retrac- 

 tion, its perfect concealment during repose, its blood-red color, and the 

 suddenness with which it can be thrown out, we must, I think, be led 

 to the conclusion that it serves as a protection to the larva, by startling 

 and frightening away some enemy when about to seize it, and is thus 

 one of the causes which has led to the wide extension and maintained 

 the permanence of this now dominant group. Those who believe that 

 such peculiar structures can only have arisen by very minute successive 

 variations, each one advantageous to its possessor, must see, in the 

 possession of such an organ by one group, and its complete absence 

 in every other, a proof of a very ancient origin and of very long-con- 

 tinued modification. And such a positive structural addition to the 

 organization of the family, subserving an important function, seems to 

 me alone sufficient to warrant us in considering the Papilionidae as 

 the most highly developed portion of the whole order, and thus in 

 retaining it in the position which the size, strength, beauty, and 

 general structure of the perfect insects have been generally thought 

 to deserve." 



It is unphilosophical, however, to accord high rank to any group 

 for a single characteristic, and especially when in nearly all its other 

 important peculiarities, it evinces its low origin. Moreover extensive 

 fleshy organs do occur in other groups. j; Guenee discovered them 

 on the abdominal segments of the caterpillars of certain blues, § and 

 caruncles, as they are called, entirely similar to osmateria in function, 

 general structure and degree of development, occur in single genera 

 of beetles, II while totally absent from their nearest allies; yet nobody 



« Wallace, Natural Selection Am. Ed. 1.35. It may be remarked that in his 

 recent work on Geographical Distribution, Wallace has abandoned his former 

 position and accepted the arrangement proposed by Bates. 



t Protrusion \s probably effected by mere contraction of tbe body-walls, 

 which fills the osmateria with the fluids of the body. 



X I have elsewhere maintained that the ventral sae on the first body-seg- 

 ment of butterfly larvae is essentially homologous with the osnjateria. See 

 Psyche I, 168. 



^ Ann. Soc. Ent. France, (4), VII, 665 seq. (1867). 



|] Malachius et al. See Siegel, Ueber den Ausstiilpungs— Apparat von Mala- 

 chius und rervandten Foruien 8'^ Hannover, 1873. 



