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such hypogene rocks as are stratified, or 

 altered by stratification ; any stratified 

 primary rock may be termed metamorphic. 

 By some authors the metamorphic rocks 

 have been divided into two groups ; 

 namely, those which present traces of 

 stratification, and, secondly, those which 

 present no appearance of regular arrange- 

 ment, but occur in amorphous or shape- 

 less masses. 



METAMO'RPHOSIS. (jufra/jojo^wcric., Gr. 

 change into another form, metamorphose, 

 Fr. metamorfosi, It.) Transformations 

 which insects undergo previously to their 

 arriving at their state of perfection. The 

 progress of metamorphosis of insects is 

 most strikingly displayed in the history 

 of the Lepidopterous, or butterfly and 

 moth tribe. The egg, which is de- 

 posited by the butterfly, gives birth to a 

 caterpillar ; an animal which, in outward 

 shape, bears not the slightest resemblance 

 to its parent, or to the form it is itself 

 afterwards to assume. It has, in fact, 

 both the external appearance, and the 

 mechanical structure, of a worm. But 

 these vermiform insects contain in their 

 interior the rudiments of all the organs 

 of the perfect insect. These organs are, 

 however, concealed from view by a great 

 number of membranous coverings, which 

 successively invest one another, like the 

 coats of an onion, and are thrown off, 

 one after another, as the internal parts 

 are gradually developed. These succes- 

 sive peelings of the skin are but so many 

 steps in preparation for a more impor- 

 tant change. A time comes when the 

 whole of the coverings of the body are at 

 once cast off, and the insect assumes the 

 form of a pupa or chrysalis ; being wrapt 

 as in a shroud, presenting no appearance 

 of external members, and retaining but 

 feeble indications of life. In this condi- 

 tion it remains for a certain period : its 

 internal system continuing in secret the 

 farther consolidation of the organs ; until 

 the period arrives when it is qualified to 

 emerge into the world, by bursting asun- 

 der the fetters which had confined it, and 

 to commence a new career of existence. 

 The worm, which so lately crawled with a 

 slow and tedious pace along the surface 

 of the ground, now ranks among the 

 sportive inhabitants of the air ; and ex- 

 panding its newly acquired wings, launches 

 forward into the element on which its 

 powers can be freely exerted, and which 

 is to waft it to the object of its gratifica- 

 tion, and to new scenes of pleasure and 

 delight. Dr. Roget, Bridgewater Trea- 

 tise. 



Transformations quite as remarkable 

 occur in several tribes of animals belong- 

 ing to other classes : such as those of the 



frog among reptiles, and of the lernsea 

 among parasitic worms. Whether the 

 higher order of crustaceans undergo a 

 real metamorphosis, has not been satis- 

 factorily proved. They are known to 

 change their shells annually ; but it has 

 not been observed that this moult has 

 been attended by any change of form, or 

 by the acquisition of any new locomotive 

 or other organs. 



METATA'RSAL. (from fierci and rapabg, 

 Gr.) Belonging to the metatarsus, as the 

 metatarsal bones, &c. 



METATA'RSUS. (from /tsrd and rapo-df, 

 Gr. metatarse, Fr.) That part of the 

 foot which lies between the ankle and the 

 toes, corresponding to the metacarpus of 

 the superior extremities. The bones of 

 the metatarsus in the most complete 

 forms of development are always five in 

 number, in each limb. 



METATHO'RAX. (from yuerd, beyond, and 

 Owpak, the chest.) In entomology, the 

 third and last segment of the thorax, re- 

 sembling the second in being of a more 

 united structure than the first. The 

 second and third segments are closely 

 united together, but the original distinc- 

 tion into two portions is marked by a 

 transverse line. To the second and third 

 segments are attached both wings and 

 legs, whereas the first segment has legs 

 alone. The third segment consists of 

 seven pieces, which are similar to those 

 of the second. The posterior wings are 

 placed at the anterior angles, and often 

 occupy the whole sides of the meta- 

 thorax. A pergamenteous partition at 

 the posterior margin, which descends in 

 a perpendicular direction, bowing in its 

 middle towards the abdomen, separates 

 the metathorax from the abdomen. 



METEO'RIC IRON. The Octaedrisches eisen 

 of Mohs ; Fer natif of Haiiy. Colour 

 pale steel-grey ; occurs ramose, and dis- 

 seminated in meteoric stones. Native, 

 or meteoric iron, is composed of iron 

 and nickel, the proportion of nickel vary- 

 ing from one to nearly ten per cent. In 

 some specimens a trace of cobalt has been 

 discovered. 



Pallas found a mass of native iron 

 1680 Ibs. in weight, in Siberia, which tra- 

 dition stated to have fallen from the air. 

 Meteoric iron is assuredly unlike any 

 iron of earthly origin, but it has been 

 imitated by fusing iron with nickel. 



METEORO'LOGY. (from /wsrswpa, meteors, 

 and \6yoc, a description, Gr.) The 

 study of the phenomena of the atmo- 

 sphere. It was not till the 17th century 

 that any considerable progress was made 

 in investigating the laws of meteorology. 



