INDIRECT INJURIES CAUSED BY INSECTS. 123 



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, micrographus, typographus, 

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

 states, in the bark of Norway fir masts imported to Southamton), Hylurgus 

 piniperda, as well as two large weevils, Pissodes notatus and pint, which 

 have similar habits, &c. &c. ; and I will conclude the list with stating as 

 a sample of the whole the ravages committed by one of the tribe, Tomicus 

 typographies, in Germany, where it sometimes attacks the inner bark in 

 such vast numbers, 80,000 being sometimes found in a single tree, that it 

 is infinitely more noxious than any of those that bore into the wood ; and 

 such is its vitality, that though the bark be battered and the tree plunged 

 into water, or laid upon the ice or snow, it remains alive and unhurt. The 

 leaves of the trees infested by these insects first become yellow ; the trees 

 themselves then die at the top, and soon entirely perish. Their ravages have 

 long been known in Germany under the name of Wurm trokniss (decay 

 caused by worms) ; and in the old liturgies of that country the animal 

 itself is formally mentioned under its vulgar appellation, " The Turk." 



ous 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 per- 

 ceptible 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 consider- 

 able examination, when they present the appearance of so many animated 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 ex- 

 ternal 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 molecules), added to their shape, which is filiform and very 

 slender, sharply attenuated at each extremity, and their hyaline colour, 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 nega- 

 tion of characters, might perhaps suffice to bring these vermicles under the genus 

 Vibrio as formerly extended by Mtiller and Bory de St. Vincent (to which, from 

 their resemblance to the so-called vinegar eels, Vibrio anguilla, 1 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 

 animal, 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 Scolytus. Their 

 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 sim- 

 plicity 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 pupae of Scolytus destructor, and 

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

 pupae of Hylesinus 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 Scolytida in the pupa 

 (and partly In the larva) state, in which, however, they do not seem materially to 

 injure them, nor prevent them from becoming perfect insects. (See Spence ia 

 Trans. Ent. Soc. Lond. ii. proc. XV.) 



