122 THE CAUSES WHICH PROPAGATE 



rings of its abdomen by collapsing- tliose behind. The air^, then, 

 it is supposed, leaving the large air-sacs, is forced as by a pair of 

 bellows into the end of the digestive canal " immediately before 

 the peculiar stomach," through a communication discovered by 

 Wagner; and traversing this, passes to the haustellum, issuing 

 by sixteen little perforations at the extremity of either of its 

 parallel tubes, as may be inferred from the air-bubbles noticed at 

 each squeak when the tip is submerged in a fluid. So may we 

 conclude the sound is really formed in the haustellum comparable 

 to two flutes joined side by side, in which nodes and loops 

 originate on expiration, augmented by strokes of the filed palpi, 

 while tlie sound waves issue at the sixteen round perforations. 

 B}^ this self-same arrangement butterflies and moths suck in 

 their nectarious nourishment. 



But the organ of crepitation is not restricted to our Death's 

 Head, Alropos. The stridulation of Acherontia Lethe is mentioned 

 by Sir Emerson Tennant in his " Natural History of Ceylon," 

 and another species from Hindustan, A. Satanas-, also squeaks, 

 according to Col. Gott. St. Pierre also mentions the stridula- 

 tion of a kind found in the Mauritius. Both male and female 

 Deaths Heads crepitate. 



Passing from the Acherontiidse to the Smerinthidse, the late 

 Mr. Walker, once employed in cataloguing at the British Museum, 

 quotes a record from Natal that a Hawk Moth {Basiana Postica) 

 " gives out sounds resembling those of a longhorned Lamia 

 beetle for minutes together." Langia zeuzeroicles, another 

 Sphinx, is described as uttering a " faint stridulous cry, like 

 that of the Death's Head, but not so loud." Then among the 

 clear-winged Sesiidce we have the musical Sesia Pelasgus, alias 

 Thjsbe, with reddish-brown wings and hyaline discs. Regard- 

 ing this, the Canadian Humble Bee Hawk Moth, Dr. George 

 Gibb says : " The sound is something like the squeaking of a 

 mouse or bat. I retained one I captured myself for some time 

 alive to hear its murmurs. This squeaking noise continued as 

 long as the creature remained alive, and was much louder than 

 in any other of the numerous Sphinges it was my good fortune 

 to capture." 



In the silk-spinning moths of the Bombycina, next in review, 

 the rule appears general that the capability for stridulation is 



