INDIRECT INJURIES CAUSED BY INSECTS. 157 



It would occupy too much space to notice in detail all the bark-boring 

 beetles which attack the various species of pine and fir-trees, which are 

 very numerous, comprising Tomicus pinastri, Laricis microgrophus, typo- 

 graphus, and chalcographus, (which I found in 1837, in the larva, pupa, and 



trunk, and thus renders the trees unhealthy before the female deposits her eggs in them.) 

 For a furtlier description of the mischief done by Scolyttis destructor, and the means of pre- 

 venting its extension, see a communication by W. S. under the article Ulmus, in Mr. Lou- 

 don's Arboretum et Frutiretum Britannicnm ; to which admirable work the reader is also 

 referred for more complete details than could be here given in the valuable contributions by 

 Mr. Westwood relative to insects injurious to this and other species of forest-trees. 



It may be here mentioned, though somewhat out of place, for the purpose of drawing 

 the attention of Entomologists to a new tribe of insect-parasites of which no account ap- 

 pears to have been giv^en in books, that in examining closely the pupae of Scohjtus destructor 

 at Brussels, I found them lined in different parts of their external surface, but especially 

 on the throat and about the cases of the elytra, with numerous transparent eel-shaped 

 vermicles, not easily visible to the naked eye from their small size, being not more than 

 one eighth or one tenth of a line in length, but perceptible through a pocket lens, especially 

 when exposure to the air or the warm breath had made them elevate their tails (or heads, 

 whichever they may be), a movement which sometimes takes place speedily, but at others 

 only after a considerable examination, when they present the appearance of so many ani- 

 mated hairs twisting and curling themselves in various directions. These vermicles, under 

 M. Wesmael's powerful compound microscope, with which he was so good as to assist me 

 in examining them, exhibit not the slightest trace either of mouth or other external organ, 

 nor of intestines, nor of internal vessels of any kind, which, if any such existed, might be 

 easily seen through their transparent skin and body. This absence of all appearance of 

 external and internal organs (the inside of the body seeming filled with granular mole- 

 cules), added to their shape, which is filiform and very slender, sharply attenuated at each 

 extremity, and their hyaline color, with very indistinct traces under a high magnifying 

 power of about twenty segments, each as long as broad, are all the characters they afford. 

 These characters, or rather negation of characters, might perhaps suffice to bring these 

 vermicles under the genus Vibrio as formerly extended by MuUer and Bory de St. Vincent, 

 (to which, from their resemblance to the so called vinegar eels, Vibrio anguilla, I at first 

 referred them,) but scarcely as it has been recently restricted by Ehrenberg, especially as 

 all his species of this genus ( Vibrio) reside in water. From their connection with an ani- 

 mal, they might be regarded as referable to the Oxyuri, were it not that neither my own nor 

 M. Wesmael's close examination could ever discover any trace of their existence in the 

 interior of either the larva, pupa, or imago of ScoJytns. TJieir wholly exterior habitat seems 

 also to exclude them from coming under Professor Owen's genus Trichina, of his group 

 Protelmintha, which, from its shape and simplicity of structure, might possibly include 

 them, but which inhabits the cellular tissue between the muscular fibres, enclosed in a cyst 

 in which it lies coiled up. Leaving it to future examination to decide the true genus and 

 relations of these vermicles, I shall here merely observe, in addition to what has been above 

 said, that I have found them upon a large proportion of the pupas of Scolytus destructor, and 

 occasionally on some of the larvae in an advanced stage of growth, and also on the pupae 

 of Hylesiiius fraxini ; and in such distant localities, and at such different periods of the 

 year, that I am persuaded that their occurrence was not accidental, but that they are true 

 external parasites, of the family of ScolytidcB in the pupa (and partly in the larva) stale, in 

 which, however, they do not seem materially to injure them, nor prevent them from becom- 

 ing perfect insects. (See Spence in Trans. Ent. Soc. Lond. ii. proc. xv.) 



Since writing the note above referred to upon Scolytus destructor, I have seen, in passing 

 through Paris to Italy, so striking an instance of the way in which the little beetle to which 

 it refers has revenged the neglect and contempt thrown upon its class by destroying in a 

 great degree the effect of one of the most vaunted and costly productions of modern archi- 

 tecture, that the fact may be worth recording as an instructive warning for the future. The 

 avenue of elms connecting the Place dela Concorde and Champs Elyseeswith the Barriere 

 de I'Etoile leading to Neuilly, St. Germains, ikc. has always been described as the most 

 magnificent approach to Paris, and was on that account selected by Napoleon for the eutrie 

 of his new empress IMarie-Louise, and as the site, at its most elevated point, of the " Arc 

 de Triomphe," commemorating his victories and companions in arms, of which he laid the 

 foundations, but which has only recently been completed at a vast expense. It is needless 

 to point out how essentially the eflect of this splendid monument of art must depend upon 

 the size, health, and beauty of the lines of trees connecting it with those which occupy the 

 Champs Elys6es and garden of the Tuilleries ; yet at this time (September 10, 18J2) there 

 are lying from twenty to thirty of their finest elms very lately cut dow-n, in consequence of 

 having died from the attacks of Scolyti ; and as many others have been previously removed 

 and replaced by young trees, and the full-grown ones offer, from their dead tops, the nume- 

 rous holes iu their bark, and the oozing sap, ample proof that their pigmy but effective 



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