KNOWLEDGE. 



[January 1, 1894. 



smaller and much duller insect than the preceding, and 

 more regularly cylmdrieal, without the curiously cut-off 

 abdomen so characteristic of Scah/tus. The economy of 



Fig. 4. — Bark Hurrowings, or " tvpogi-apli " of Hiflesiiiu-ifrnxina, Ash- 

 bark Beetle, a. motlier crallery ; 6, larral galleries (To avoid con- 

 fusion, the larral galleries of one system only have been shown.) 



this insect is very similar to that of .s. destructor, but the 

 male takes a somewhat more practical interest in the 

 serious business of life. Both beetles may be found in the 

 burrows during the course of construction, frequently one 

 in each bi-anch, and of course it is an obvious suggestion 

 that one of tbese branches is made by the male, and the 

 other by his partner ; but it is difliciilt to say how much 

 truth there is in such a suggestion, and it seems not un- 

 likely that even in this ease the female dees the greater 

 part of the work, though apparently her mate does some- 

 thing to assist. Both beetles also usually die in the burrow, 

 and their corpses may sometimes be foiind still lying there 

 several years after death. Damp and mildew, however, in 

 time do their work, and the corpses decay and disappear. 



The other members of this group are more or less like 

 those already described, and the cylindrical form, short legs, 

 and large thorax will usually enable them to be recognized. 

 They attack a variety of trees, some devoting their atten- 

 tion to the trunk, others to the branches and smaller 

 twigs. Elm, ash, oak, beech, birch, hazel and hornbeam 

 are all more or less liable to attack, and fruit trees, such 

 as apple, pear, plum, cherry and apricot, are by no means 

 exerupt. A large proportion are devoted to the different 

 species of firs and pines, and some attack shrubs, such as 

 ivy, furze, and broom. But wherever they are found, they 

 always leave their signature behind, in the typograph on the 

 inner surface of the bark, and its fainter reproduction 

 which is seen on the wood when the bark is removed. 

 Until an affected tree is stripped, the e^'idences of their 

 presence, apart from any sickly appearance the tree may 

 present, are not striking, and the slight indications outside 

 can give no notion of the vast extent of the damage which 

 may lie concealed within. These little beetles must be 

 carefully distinguished from another set of wood-borers, 

 some of which are not unlike them in both shape and 

 general appearance, but which do not leave a typograph 

 behind them, since they burrow into the substance of the 

 wood itself, uistead of confining themselves to the bark. 

 Belonging to this latter group is the troublesome household 

 pest which makes furniture " worm-eaten " (Anohium 

 ilomesfinim). Wood-borers such as this are distinct from 

 the liark-borers, not only in habits, but in structure too, 

 and are therefore, for systematic purposes, placed in a 

 different section of the beetle order. 



There are two somewhat opposing aspects in which 

 these bark-boring beetles may be regarded. In the first 

 place, in so far as they attack living trees, they cannot be 

 regarded as otherwise than terribly destructive. Though 

 the solid timber, it is true, is scarcely injured at all, and 

 the actual amount of material destroyed bears a ridi- 

 culously small proportion to the total bitlk of the tree, yet 

 the death of the tree is insured by the fact that it is just 

 the most vital part that is attacked. The centre of the 

 life and growth of the tree lies in the layers which 

 intervene between the hard bark on the outside and the 

 hard wood on the inside ; it is here only that the cells of 

 which the tree is composed still remain soft and retain 

 their power of self-multiplication, and therefore, so long 

 as this particular part of the tree is intact, its functions 

 can go on more or less regularly, and its life can be 

 maintained. But when once these layers are tampered 

 with, the health of the tree suffers, and the gradual re- 

 moval of the growing and multiplying tissue is necessarily 

 followed by the death of the tree, though the solid timber 

 is still available for use. In consequence of their enormous 

 numbers, some of the smaller species are in this respect 

 even more destructive than the larger ones. 



There is, however, another light in which the ravages 

 of these insects may be regarded. In many cases, no doubt, 

 they merely accelerate the destruction of trees which 

 from other causes are passing into decay, while some seem 

 to prefer fallen timber to that which is growing ; and it is 

 in this latter respect that they may to some extent be 

 regarded as useful agents in the economy of nature. In 

 the interests of surrounding vegetation, it is important that 

 fallen trunks should be removed as speedily as possible, 

 and many are the natural agencies that combine to bring 

 about such a result. Amongst these, damp is of course 

 one of the most important, as it provides the conditions 

 necessary for the growth of fungi, which, growing on the 

 wood, derive their nourishment from it, and accelerate 

 its dissolution. But much of the material of which the 

 bark is composed is of the nature of cork, and is impervious 

 to moisture, so that as long as the bark remains on the 

 tree the fungi have not a fair chance. To meet this 

 difficulty, there come in these bark-feeding beetles, which 

 speedily loosen the bark and cause it to crack so that it 

 soon falls off", and then the solid wood is exposed to all 

 sorts of destructive agencies — whether physical such as 

 damp, vegetable such as fungi, or animal such as wood- 

 boring insects — and between them they make short work 

 of the trunk. In virgin forests, no doubt, such insects as 

 these are of material assistance in promoting the growth 

 of new vegetation, by aiding in the removal of the old. 

 In countries like our own, however, which are well under 

 the control of man, such a function is, no doubt, scarcely 

 needed, and to us these bark-boring beetles seldom appear 

 in any other light than as a nuisance. 



PERIODICAL COMETS DUE DURING THE 

 REMAINDER OF THE PRESENT CENTURY. 



By W. T. Lynn, B.A., F.R.A.S. 



IT can scarcely be said that any one of the known 

 periodic comets is due during the present year. The 

 late W. Tempel was the first discoverer of no fewer 

 than three comets which were calculated to be 

 moving in orbits of short period ; but the periodicity 

 of one of these, which was discovered in the month of 

 November, 18G9, was not recognized until after its re- 

 discovery by Prof. Swift in 1880 (an unobserved return 

 must have taken place in 1875), in consequence of which 



