Mr. Foggo on an Insect found in the wood of' a Table. 87 



its confinement, and what are the causes which have retard- 

 ed its advancement, to maturity. A late author has conjectur- 

 ed, that the ovum from which the insect was produced, hav- 

 ing been prevented from undergoing the necessary evolution, 

 had retained its animating principles till summoned into ac- 

 tion by some change in its relation to external objects ; and 

 further, that it might have lain dormant for an indefinite 

 space of time. The same author has likewise endeavoured 

 to explain in this manner the periodical visitation of the lo- 

 cust, palmer worm, Hessian fly, #c. with the additional hy- 

 pothesis that certain modifications of the atmosphere may be 

 peculiarly favourable for their production. This explanation, 

 however, is liable to several objections. It is difficult to con- 

 ceive any cause that could operate year after year in pre- 

 venting the animal from arriving at maturity, and that too, 

 apparently in the very situation selected by the instinct of 

 the mother. Moreover, on examining the cavity in which 

 this animal was lodged, it is evident that, while within the 

 tree, it must have passed its life in an inert state. This is a 

 fact which is scarcely consistent with our knowledge of the 

 economy of insects, for they are, I believe, always most vora- 

 cious in the larva state. It is, therefore, most probable, that 

 the larva penetrated the tree in order to prepare for becom- 

 ing a chrysalis, and having at last assumed its perfect form, 

 emerged into light in the usual time. That the insect made 

 its appearance in the ordinary period peculiar to the species, 

 is rendered probable from several collateral facts. It is well 

 known that several species of insects remain in the chrysalis 

 for many years; that the locust appears in numbers, once on- 

 ly in 17 years, and the palmer worm in 30 years, yet these 

 are cycles not recognised by meteorologists. The tribe Uro- 

 cerata is also subject to periodical swarming, " et paraissent 

 certaines annees en telle abondance quils ont etc pour le peuple 

 tin Btijet d'efFroi." Mr. Marsham mentions, that several in- 

 dividuals of the Urocerus Gigas issued from the planks 

 forming the floor of a bed-room. A solitary individual of 

 the U. psyllius was taken in the neighbourhood of Edinburgh, 

 which very likely found its way into this country by a simi- 

 lar means. 



