April 1, 189S.] 



KNOWLEDGE. 



85 



Fig. 



3. — Larva of 

 chafer. 



Cock. 



The larvffi of certain beetles live habitually underground, 

 where some of them feed upon roots, while the rest prey 

 upon other subterranean creatures. A rrot-feeder, such 

 as the common cockchafer (Fig. 3), which lives for three 

 years as a larva, retires deep into 

 the ground during winter, where 

 its soft body is removed from the 

 chilling influences of the winter 

 winds and frosts ; and being 

 below the level of the roots on 

 which it is accustomed to feed, 

 it of course spends its time 

 fasting. In such a case the 

 change into the pupa state occurs 

 in the last autumn of the insect's 

 existence as a grub, and the perfect insect appears in 

 the following May or -June. But its first appearance 

 as a beetle above ground by no means coincides with the 

 time of actual change into the perfect insect. This 

 has taken place long before, in the subterranean cell 

 it had excavated for itself, and where it has remained 

 quiescent till its armature is hard enough to encounter 

 safely the rebufl's it will meet with in pushing its way up 

 through the soil, and during its subsequent career above 

 ground. The handsome green rose-beetle already referred 

 to, whose larva is very similar to that of the cockchafer 

 and has corresponding habits, becomes a perfect insect in 

 its subterranean cell in the autumn, though it does not 

 appear in the open air till the roses are ready for it in the 

 following June. 



Summarizing what has been said, we see that the 

 absence of insect life in winter is illusory so far as the 

 Coleoptera are concerned ; if we had powers of vision that 

 could penetrate their hiding-places, we should see that 

 every part is weU stocked with life. Under the piles of 

 dead leaves that strew the ground around trees or at the 

 foot of hedges, under bark, stones, or clods of earth, in 

 fallen twigs and hollow stems of plants, in tufts of grass, 

 in the sohd wood of trees and the fungi that grow on them, 

 and even under the soil itself, there would be revealed 

 beetles of the most varied kinds ; and if all these could 

 suddenly be laid bare at once, we should be astounded at 

 the multitude of living forms that are existing, all unknown 

 to us, around us on every hand, waiting in a more or 

 less torpid condition tUl the returning warmth of spring 

 summons them to renewed activity, and for the great task 

 of preparing for the generation that is to succeed them. 

 ( To be continued. J 



ilcttrrs. 



[The Editor does not hold himself responsible for the opinions or 

 Btatements of correspondents.] 



THE "HOOP SXAKE." 

 To tlie Editor of Knowledge. 



A coiTespondent writes as follows:— "In the Rocky 

 Mountains there is said to be. besides the rattlesnake, 

 another of a comparatively small kind, which has the habit 

 of living on the hill- tops, and when about to attack tak s its 

 tail in its mouth and trundles down the declivity, earning 

 from this peculiarity the name of ' hoop snake.' Is this a 

 fact, or one only of the great series of travellers' tales ? " 



The existence of this phenomenal snake is one of those 

 superstitions which, like the relation of the great toe to 

 lock-jaw, is of curiously world-wide prevalence. The hoop 

 snake is to be heard of in Australia, in the River Plate, in 

 Ceylon, at the Cape, and in many regions of the United 

 States. Our correspondent presents us with a very tame and 



prosaic specimen of this mythical genus, inasmuch as it does 

 no more than " trundle " passively d^wn-hill by the mere 

 law of gravitation ; whereas more liberally-inspired observers 

 have recorded its progress on the flat by virtue of its own 

 proper volitional force at a speed which, in one instance, 

 carried destruction to two horses ploughing, and in another 

 was sufficient to split the trunk of a tree ! Fortunately, we 

 have here to deal with a question of anatomical fact, not 

 an issue of disputed evidence like the allegation of the 

 viper swallowing its young for protective reasons. The 

 conformation of a serpent's spine is such that it could not 

 assume the position indicated, owing to the interlocking of 

 certain bony processes of the vertebrje. Unlimited as the 

 creature's flexibility of body may appear to be, it will be 

 found on analysis to lie almost entirely within the scope 

 of its lateral movements. This is well illustrated ly its 

 actions as it passes in and out between the bars in 

 ascending a ladder. Its faculty of flexion in an antero- 

 posterior direction is in reality very limited indeed, and is 

 represented to about its fullest extreme in the " sitting " 

 attitude of the cobra di capdlo. It would be impossible, 

 therefore, for a serpent to take its tail in its mouth when 

 in this position. We find in this an exact converse to the 

 structural position which obtains in the vertebral columns 

 of many higher animals — the whale, for instance, whose 

 spinal mechanism admits of considerable undulation from 

 behind forward or up and down, but in which the trans- 

 verse projections of bone, or processes, would jam and 

 effectually prohibit anything like lateral motion. Not 

 only are hoop snakes postulated by the public, but at least 

 one work on popular natural history of the present day — 

 one, moreover, admirable in all its matter antecedent to 

 the Reptilia — actually describes a "looping" mode of 

 progression of serpents analogous to that of a caterpillar ! 

 More remarkable still, no volume of zoology, to the best of 

 my belief, makes mention of that movement which a 

 hurried or alarmed snake adopts, apparently with the view 

 of eluding the grasp or blow of an aggressor by confusing 

 the vision rather than by attaining speed, and which 

 deserves par excellence the title of " serpentine." 



,,, Akthub Stbadlkg. 



THE SODIUil EADIATIOX. 

 To tlie Editor of Knowledge. 



Sir, — If you will allow me to continue this discussion, 

 I should like to make a few further observations in reply 

 to the remarks of M. Deslandres, in his very interesting 

 letter in the March number of Knowledge, on the electric 

 origin of the chromosphere. 



I will confine my remarks to the question of the origin 

 of the D line, with regard to which a certain sense of 

 conviction has arisen in my mind as the result of long- 

 continued experiments on the radiation of heated sodium 

 vapour and other gaseous bodies. 



To begin with, I may say that the much greater width 

 of the D line in the heated tube, as compared with the 

 line seen in flames, is certainly due to a greater density of 

 vapour in the former. This, as M. Deslandres admits by 

 his question, distils unchanged from the hot to the cooler 

 parts of the tube. 



I do not rely entirely on this difference of width, 

 however, to prove my point, but also, as explained in my 

 previous letter, on the exact correspondence between the 

 emission and absorption lines, show;ng that practically 

 every free sodium molecule in the hot part of the tube shares 

 in the light emission, wh.ch must, therefore, be due to some 

 other cause than chemical change in the ordinary sense. 



M. Deslandres suggests allotropic changes at high tem- 

 peratures — in other words, interchanges between the atoms 



