Maixcii 1, 18GG.] 



SCIENCE-GOSSIP. 



57 



«lfc* 



repairs done have efl'ectually barred their exit from 

 the woodwork of the floor. The Micrographic Dic- 

 tionary says, " This active little insect, which runs, 

 but does not jump, is found (in the country) upon 

 the shelves of cupboards, where sweets and other 

 eatables are kept, in window cracks, &c. Its habits 

 are nocturnal." 



A relative of the Lepisma sacchariua, frequenting 

 the rocks at the sea-side, and very like it in appear- 

 ance, gives a very different scale. 



The Podura scale still holds its ground as a 

 genuine test for penetration in a good i or § object 

 glass. The insect from which it is obtained is about 

 the size of a flea, and is to be found in cellars. 

 There are many species inhabiting various localities. 

 I have found one sort under damp stones and 

 flowerpots at various times, which gives tests of 

 extreme difficulty. This species glows with irides- 

 cent colours, and is very small. Another kind, and 

 perhaps the most suitable for the purpose of display 

 or trial, inhabits drier places, and often, in the sum- 

 mer time, makes its appearance in the house, under 

 unexpected circumstances ; such as hopping on the 

 book you are reading. It is either silvery-white 



or dark-grey. 

 Dr. Carpenter 

 says, "Its scales 

 are of different 

 sizes, and of dif- 

 ferent degrees of 

 strength of mark- 

 ing, and are by 

 no means of uni- 

 form value as 

 tests. The gene- 

 ral appearance of 

 their surface un- 

 der a power not 

 sufficient to re- 

 solve their mark- 

 ings is that of 

 watered silk, 

 light and dark 

 bands passing 

 across with wavy 

 irregularity ; but 

 a well-corrected 

 lens of very mo- 

 derate angular 

 aperture now suf- 

 fices to resolve 

 every dark band into a row of short lines, each of 

 them being thick at one end and coming to a point 

 at the other, so that the impression conveyed is 

 that of a set of spines projecting obliquely from the 

 surface of the scale like the teeth of a ' hackle.' 

 A more careful examination of the scales, however, 

 of which the superficial layers have been removed, 

 serves to show that these dark lines are but the 



Stilt 

 Mm wffii tip 



ill! 



la i 



Fig. 63. Scale of Podura x 450. 



spaces between the minute wedge-like particles 

 arranged side by side, and end to end, of which 

 those layers are made up." The directions copied 

 from one book into another about catching these 

 insects with oatmeal or flour, I fear, are not of 

 much value ; at least, I never succeeded myself in 

 that manner. I believe they may be found in every 

 cellar or damp cupboard, and I have never experi- 

 enced any difficulty in finding them. 



When obtained, they must not be touched by the 

 hand, or the scales will be rubbed off. Having 

 induced them to enter a pill-box, the insertion into 

 it of a little piece of blotting-paper saturated with 

 chloroform will effectually kill them. If chloroform 

 be not at hand, the sulphurous vapour from a 

 lighted lucifer-match will do as well. 



The writer's humble opinion with respect to the 

 scales of insects, as tests, is, that they are invalu- 

 able, inasmuch as they show the penetrative power 

 of the object-glass while the markings on the more 

 difficult Diatomacese test its definition. In high- 

 power object-glasses of inferior quality one or other 

 of these requisites fails. 



Fig. 64. Scales of Curculio of the Beech x 350. 



The elytra of many Curculios, British as well as 

 foreign, arc worthy of being mounted. I, like 

 many others, have endeavoured to discover the 

 cause of their splendour, but am unable to throw 

 much light on the subject. The scales of both 

 British and foreign beetles were examined, first in 

 the dry state, both by transmitted and reflected light, 

 and also by dark-ground illumination. With the two 

 former modes of display the colours were strongly 

 marked. Under a ? objective by Ross, and with 

 transmitted light, rainbow tints were present in each 

 scale, rendering it very beautiful; something like 

 the phenomena of polarized light. This was 

 particularly the case with the scales from the 

 Diamond Beetle of Brazil, which resembled a piece 

 of selenite of varied thickness under the polari- 

 scope; the different colours being quite as bright, 

 and bounded apparently by either cracks in the 

 surface or breaks in the laminae composing the scale, 

 just like that mineral, or like the pieces of stained 

 glass in a church window. When dark-ground 

 illumination was adopted by means of the parabolic 



