215 



INGA. 



INSECTA. 



216 



rucks, and abundant in the upper tertiaries. It is true that Ehren- 

 berg, by assigning to the cretaceous era the calcareous marls of Oran, 

 Sicily, and Greece, gives a large catalogue of Mesozoic Infusoria, and 

 that in favour of such reference of those marls are the Botalitx, Tex- 

 tilince, &c., which occur both in the true chalk and in such marls. 

 But on the other hand, remembering the long scale of geological time 

 through which these genera of Polythalamia; extend, and taking into 

 consideration the fact that some species which occur in the chalk of 

 Europe are quoted by Ehrenberg from unquestionably miocene strata 

 in America, we shall hesitate to admit those richly infusorial marls as 

 truly coeval with the white chalk, in which comparatively very few 

 remains of the group occur, and these not of the same species as 

 those which abound in the other deposits. 



Another point on which the authority of Ehrenberg has not been 

 received without hesitation, is the absolute specific identity of a large 

 proportion of the fossil and recent Infusoria. The previous dis- 

 coveries of geology had prepared an easy admission for the opinion 

 that many of the tertiary forms of Infusoria were undistinguishable 

 from living races ; such is the fact in regard to all the iavertebral 

 races ; but with very few and those not always allowed exceptions, 

 the secondary strata had been found to contain only extinct forms of 

 life, till Ehrenberg examined the minute Polythaiamice, and found 

 many of them similar to living types, and confirmed this inference by 

 independent researches among the Infusoria. Supposing these 

 opinion.- of the Prussian microscopist to be confirmed by future 

 inquirers, we shall find that they involve no infraction of the relations 

 of zoological forma to geological time, which have been established 

 from examinations of the other classes of the animal kingdom. The 

 systems of life in each successive system of strata are not separate 

 and distinct creations, but successive terms of a creative series ; each 

 of these terms is compound, and (to speak exactly) its constituent 

 quantities (the several classes, orders, families, genera, or species) have 

 their own coefficients and exponents ; that is to say, have their own 

 times of duration, their own periods of abundance, their own peculiar 

 relations to earlier and later organisations. 



A rule drawn from Fishes cannot be applied to Mollusca; a law 

 based on Crustacea cannot be received for Microzoaria, without scru- 

 pulous examination; and palaeontology is full of examples of the 

 unequal periods of duration which belong to the different organi- 

 sations, and the unequal degree of development and unequal 

 geographical diffusion which characterise these organisations at the 

 same epochs and during the same periods. 



Admitting the authority of Ehrenberg's determination of species, 

 we find another curious and unexpected result the frequent, if not 

 general, admixture of marine and fresh-water tribes in the compara- 

 tively level regions of Europe. In the plains of North Germany, 

 round the Bohemian and Harz Mountains, in Tuscany, and Yorkshire, 

 we find this admixture of supposed marine and supposed fresh-water 

 races in the supra-tertiary deposits. Is this to be explained by sup- 

 posing those deposits to have happened while the relative level of land 

 and sea wag different from what it is at present, and the sea was near 

 to the place of deposition, so that by some of the many natural modes 

 of diffusion which are effective in this class of life the organisms of 

 the sea might be carried into lakes, as well as mixed in sestuaries, and 

 along the course of languid rivers ? Probably so. The deposits of 

 J nfusoria which now happen so abundantly at the mouth of the 

 Elbe are mostly derived from the sea ; and it has been found in the 

 river Hudson that species once imagined to be truly marine live in 

 juxtaposition with the species of fresh waters. There may probably 

 be, in a class of beings associated with silicated waters, a greater 

 independence of the saline qualities of water than in other races 

 which have little need of silica, and which require the extrication of 

 lime from a state of solution in the waters which they inhabit. In 

 confirmation of this view we find the Sponyia of the sea matched by 

 the Sportrjillre of fresh water, each extracting silica from the liquid, 

 but the calciferous Polypean races of the ocean are almost unrepre- 

 sented in our inland lakes and streams. 



(Ehrenberg, Itie Jnfaiionsthierchen ; Memoir! of the Berlin Academy, 

 and Translations in Taylor's Scientific Memoirs; Reade, Quekett, 

 Roper, Brightwell, Gregory, and others, in the Microscopic Journal, 

 and Quarterly Journal of Microscopical Science ; Mantell, Medals of 

 Creation and Annals of Natural History ; Pritchard, Infusorial 

 Animalculti ; Owen, Lectures on Comparative Anatomy; Carpenter, 

 Principle* of Physiology ; Dujardin, Histoire det Zoophytes Infusoires; 

 Stein, Die hfusionsthiere, &c.) 



INGA, a genus of Plants belonging to the natural order Leyu- 

 minosce, which, though it has been separated from Mimosa, yet contains 

 upwards of 100 species. These are found in the tropical parts of Asia, 

 Africa, and America. They are distinguished by their legumes being 

 broadly linear, compressed, and 1-celled. The seeds are usually 

 covered with pulp, more rarely with farinaceous matter or a pellicle. 

 The species form shrubs or trees, and are commonly unarmed. The 

 flowers re in spikes, or are capitate, and of a red or white colour. 

 From the number of species in this genus, as well as in A cacia and 

 Afimosa, and from their having been removed from one to the other, 

 there is some confusion in the synonyms. A few of the useful species 

 have been further separated into the genus Parleia ; but many still 

 remain which are important in the countries where they are indige- 



nous, either for astringent properties, like many Mimosas and Acacias, 

 or for the edible nature of the fecula or pulp which surrounds their 

 seeds. Thus I. cochliocarpus has bitter and astringent bark, which is 

 used in tanning and also in medicine. It is taken to Portugal, where 

 it is called the Brazilian Bark, and used even as a substitute for that 

 of the Cinchona. Martius distinguishes from this species, which he 

 calls /. Jurema, another which he has named /. astringms, and of 

 which the bark has similar properties. The bark of these trees is 

 considered by some authors to be the Cortex Astringens Brasiliensis 

 of old pharmacopoeias. /. salutaris is another astringent species, a 

 native of New Granada, of which the bark is much used in the form 

 of decoction for various complaints in which astringents are indicated, 

 and for the same purposes as Ratany Root. Some of the species, as 

 before mentioned, are esteemed for the sweetish edible pulp with 

 which their seeds are surrounded, as I. didcis in India and /. insignia 

 in the province of Quito, where it is called Guabo, or Guabas, but 

 Pacaes in Peru. So /. Camatchili, according to Perrotet, is similarly 

 esteemed in Manilla, and /. Faroba in Western Africa, in the neigh- 

 bourhood of the Senegal. /. i-era contains taunic acid, and is one of the 

 numerous leguminous plants used for obtaining Catechu. The pulp of 

 the fruit of this species also is purgative. /. fceculifera yields in its 

 pods a laxative pulp called Pois-Doux in St. Domingo. It has a 

 sweet taste. The pulp also of the pods of /. tetraphylla is sweet and 

 mucilaginous. (Lindley, Vegetable Kingdom.) 



INIA. [CETACEA.] 



INOCE'RAMUS (Sowerby; Goldfuss), a remarkable genus of 

 Fossil Conchifera monomyaria, allied to Crenatula, Genillia. &c., 

 originally named by Mr. J. Sowerby in the ' Linn. Trans.' The name 

 Catillui was given to the larger species by M. Brongniart. The two 

 valves approach to equality ; both are convex ; the hinge-line straight, 

 often extended into a wing, and thickened with many transverse 

 grooves to receive a divided ligament ; shell fibrous ; beaks recurved. 

 Inoceramus dubius occurs in the Lias ; /. concentricus in the Gault ; 

 /. Cuvieri and many other species in the Chalk. 



INSECTA, one of the classes of Invertebrate Animals. The Latin 

 term Insecta, like the Greek Entoma, which has been applied to these 

 animals, has reference to the insected or divided appearance of the 

 body ; hence the English name Insect, the French Insecte, and the 

 German Insect. Invertebrate Animals are divided by Lamarck into 

 two groups, which he calls Animaux Apathiques, and Animaux 

 Sensibles. The latter, or the Sensitive Animals, contain six classes, of 

 which Insects are the first. According to Latreille's arrangement hi 

 the ' Regne Animal,' the class Insecta forms the third great division 

 of articulated animals articulated referring to the innumerable 

 joints of which this class of animals is composed. 



True Insects may be thus defined : Articulated animals possessing 

 six legs, two antenna;, two compound eyes ; a small brain at the 

 anterior extremity of a double medullary chord. Circulation effected 

 by a pulsating dorsal vessel provided with numerous valves. Respi- 

 ration by tracheae, which form two lateral trunks, and ramify through 

 the body; generation oviparous; two distinct sexes; adult state 

 attained through a series of metamorphoses. 



Insects generally possess two pairs of wings ; the trunk in the adult 

 animal is usually composed of three chief parts, the Head (Caput), 

 Thorax, and Abdomen ; or the trunk of an insect may be described 

 as consisting of thirteen segments, of which one constitutes the heau, 

 three form the thorax, and the remaining nine compose the abdomen. 

 The head includes the organs of sensation and manducation, and its 

 principal parts have received the following names : the Clypeus, 

 Vertex, Occiput, Gense, Cauthus, Gula, Oculi, Stemmata, Antenna;, 

 and the Trophi. 



Fig. 1. 



Fig. 1, the Hornet, magnified; a, the head (caput) ; I, b, the thorax ; c, the 

 abdomen ; d, d, antenna). 



The Clypeus is that part of the upper surface of the head which 

 joins the labrum. It is called by Kirby nasus, and in the Lamelli- 

 comes it is usually the foremost part of the head when viewed from 

 above. 



The Vertex is the summit of the head. 



