124 THE CAUSES WHICH PKOPxiGATE 



establish its presence very generally among* the lichen-feeding 

 Litlwsiida, as well as in the Tiger Moths^ whose palmer-worms 

 are herbivorous ; its development attaining a maximum perhaps 

 at the tangential point of these two beautiful groups. Guenee 

 describes this identical vesicular inflation in several Alpine 

 species or sub-species of little orange moths {Setina) /^ some 

 of which he describes as producing ticking sounds like a 

 watch when placed to the ear. We may see it too in the 

 indigenous species of this family that propagates on the 

 lichened bark in forest glades, and trace it in other genera. 

 Dissections of the striated vesicle have shown it to be empty, 

 and divided into a right and left cavity by a membranous 

 partition. Fear and anger appear the stimuli to music in the 

 Heterocera now noticed; but the stridulation of others has 

 greater range of expression. 



We will now proceed to consider the cry emitted by the 

 common green Silver-hnes (Plate IV., Fig. 3, a). Tbis insect, 

 whose arboreal life and propensity for uttering a queer squealing 

 on the wing, that, heard in the early spring evening, seems the 

 oracle of that mystery which history has ever shrouded in the hush 

 of its oaken shades, once had a very wide geographical distribution, 

 specimens coming to us even from Australia. It has likewise an 

 unstable position in classification. A green obliquely-striped 

 caterpillar, recalls the Hawk Moths; a boat-shaped cocoon, a 

 mobile family of the FyralicUna ; and the moth itself has a 

 general resemblance to the Noctiiina, Pi/ralidina, and Blunt 

 Wings, in all of which groups it has done duty. The partiality 

 of the male for flying around bushes, solitary or toying with its 

 female whilst uttering its cry, that has been compared to that 

 of the Woodman Beetle, and may be likened to the fitful and 

 rasping sound of the bat, taken in conjunction with the emerald 

 scales which adorn its primary wings, presents a striking micro- 

 cosm of the parrots among the palms of the tropics. The first 

 notice of its stridulation is found in jNIorris^s '' British Moths. ^■' 

 '^ I wrote,^^ says this gentleman, '' of my own knowledge; I 

 remember the time, place, and circumstance well. I was then at 

 Bromsgrove School, and was out ' hunting ' one evening ; and I 



* Aiirita, Ramosa, Roscida, Irrorca, Flavicans, and Andereggi. 



