244' THE CAUSES WHICH PROPAGATE 



may perhaps be regarded as representing a eustachian tube, 

 I have noticed this organ developed in moths of the Bombycina, 

 Noctuina, and large Geometrina; but in Sphinx Moths and 

 Butterflies it appears as a rule absent^ or barely indicated. 



Among these, it is found most readily in the night-fliers, 

 where its position is unvarying, and its parts are identical and 

 readily recognisable, with only a variation of form according to 

 species ; so that here it seems to impress a constant anatomical, 

 in addition to a well-marked superficial, character. 



To examine this structui-e, we may capture any large summer 

 species of these moths, such as the Dark Arches, the Cabbage 

 Moth, or the common "Dagger,^'' the former to be found 

 commonly reposing by day under copings in gardens, and the 

 last, equally frequently, concealed on untarred and licheny 

 palings — or, still better, if we can procure from willows in 

 the neighbourhood a supply of the larger autumnal Red- 

 underwing Moths, Then, having killed our insect, cut oif the 

 wings, and denuded the posterior portion or abdomen of its 

 feathery scales and hair^ on proceeding to examine this part 

 in front, at its attachment to the last segment of the thorax, 

 we are at once struck by a remarkable constriction in the 

 segments (Plate V., Fig. 8), that seems to have had its origin 

 during the metamorphosis of the crawling caterpillar to an 

 insect fitted for aerial locomotion. As to how this has been 

 accomplished, it would seem there may be some latitude of 

 opinion; but from a fortuitous dissection made of a caterpillar 

 just previous to transformation, which allowed me to remove, 

 as I believe, a sentient chrysalis from the larval body, I myself 

 incline to a notion of obsolete generation in opposition to the 

 little-understood theory of development by Ecdysis, or the 

 mere shedding of envelopes; and the transformation, therefore, 

 I would seek to explain in this way. Beneath the intestinal 

 canal, or from the stomach {?) of the caterpillar, with its thirteen 

 equal segments, there originates a chrysalis, which, nourished on 

 the substance of its parent, who leaves off eating and mopes, 

 and supplied with air by a set of tracheae from its spiracles, 

 grows and increases in size, till it is sufficiently distended to 

 totally occupy to the skin of its progenitor who, his internals 

 being then consequently consumed, becomes defunct. 



