MEANS OF DEFENCE OF INSECTS. 265 



One of them, described by De Geer, is very remark- 

 able. It consists of a small, tliickish, circular lamina 

 of brown silk, becoming- as hard as gum, whicls exactly 

 fits the aperture of the case, and is fixed a little within 

 the margin. It is pierced all over with holes disposed 

 in concentric circles, and separated by ridges which go 

 from the centre to the circumference, but often not 

 quite so regularly as the radii of a circle or tlje spokes 

 of a wheel. These radii are traversed again by other 

 ridaes, which follow the direction of the circles of 

 holes ; so that the two kinds of ridges crossing each 

 other form compartments, in the centre of each of 

 which is a hole''. 



Under this head I shall call your attention to another 

 circumstance that sav^es from their enemies innumera- 

 ble insects : — 1 mean their coming forth for fiight or for 

 food only in the night, and taking their repose in va- 

 rious places of concealment during the day. The in- 

 finite hosts of moths {Phalxna^ L.), — amounting in 

 this country probably to a thousand species, — with few 

 exceptiojis, are all night-fliers. And a considerable 

 proportion of the other orders, — exclusive of the Hi/- 

 menopiera and Diptera, which are mostly day-fliers, — 

 are of the same description. Many larva; of moths also 

 come out only in the night after their food, lying hid 

 all day in subterraneous or otlser retreats. Of this 

 kind is that of Noctua pidla and Nj/ctcrobius, whose 

 proceedijjgs have been before described''. "The cater- 

 pillar of another moth (Noctua siiblerranea, F.) never 

 ascends the stems of plants, but remains, a true Troglo- 



" Reaum. iii. no. De Geer, ii. 519. 545. Platr XVII. Fk. 1 1. 

 » Vol, I. 2d Ed. 456. 



