In the ARTICULLTA (ITOMOGANGLIATA, Owen), brains, or ruling ganglionic centres, for the first time make their appearance in a suffi cient state of development to correspond with organs of sense of a localized character, or to animate systems of muscles adapted to wield locomotive limbs, and combine complex ac tions now essentially connected with the more perfect attributes bestowed on forms of life capable of more extensive relations with sur rounding objects. Still, however, an exact correspondence exists between the progressive expansion of the nervous centres and the gradual appearance of limbs moved by a distinct mus cular apparatus, which become progressively superadded to the annulose body or trunk of the articulated animal, and in precisely the same manner does the advancement of the nervous system from a less perfect to a more concentrated condition evidently precede the appearance of external appendages, subservient to the exercise of more exalted powers of sen sation, or increased capabilities of locomotion. The humblestannulose forms, as for example the Leech and the Earthworm, possessing, as they do, a nervous system consisting of an extended series of numerous pairs of feeble ganglia, none of which are as yet sufficiently potent to con trol any complex muscular apparatus, or to appreciate impressions derived from without with much nicety orprecision,are necessarily deprived of outward limbs, or complicated instruments of sense ; their soft and flexible integument is unequal to sustain any jointed members what ever, and the first rude vestiges of simple eyes, ocelli, are all that can be allowed for the pur poses of vision. By degrees the nervous gan glia becoming fewer in number as they coalesce into larger and proportionately more energetic masses, the moving organs of the body become perfected in the same ratio; limbs, almost impotent as yet, but still sketching out the arti culated legs hereafter to be perfected, make their appearance, and the apodous Annelidan, the humble inhabitant of the water, is promoted to a terrestrial existence ; jointed filet at length become appended to the segments of the still worm-like body, small and feeble at first, as in the Lulus terrestris and the other vegetable eating MTRIAPODS, but speedily, in proportion as the individual segments of the body become enlarged and strengthened, and the motor gan glia acquire increased energy, assuming larger dimensions and greater perfection of structure, until the annulose animal attains the strength and activity of the carnivorous Scolopendra, and becomes fitted for a life of rapine and destruction.
Advancing from the Scolopendra, which as yet is only able to creep upon the surface of the ground, we are at length conducted to the far more active and highly gifted races of Iesecis, properly so called, in which the de velopment and perfection of the muscular sys tem is advanced to a condition adapting these wonderful little beings to an aerial existence, and in making the transition from Myriapod to the Insect the carrying out of the same great law is most obviously and conspicuously illustrated. The nervous ganglia, still nume rous and proportionately feeble even in the Scolopendra, become in the aerial insect reduced in number until they are collected into a few large and potent masses ; senses of a wonder fully exalted description, correspondent with the increased size of the encephalic ganglia, replace the simpler organs of the less exalted Articulate; those segments of the body where unto locomotive members are appended coalesce and become fused together into a dense and strong thoracic armour able to sustain the vio lent efforts of the powerful muscles now re quired for flight; the corresponding ganglia contained within the thorax exhibit a size and development proportioned to that of the mus cles they are destined to animate ; and the winged Insect becomes thus competent to the exhibition of feats of strength and activity not to be paralleled in any other race of living beings.
On taking a survey of the molluscous or of the vertebrate divisions of the animal creation, the same great law is every where apparent, and we are reminded, on all hands, that a strict parallelism exists between the condition of the locomotive system, whatever may be its cha racter, and the perfection of the nervous appa ratus, whereby muscular movements are con trolled and directed. As a necessary conse quence of the above intimate and inseparable relation, which invariably exists between the organs of motion and those of innervation ; and allowing, as modem Zoologists all admit, that the nervous system, whatever may be its condition, is to be regarded as the ruling pri mary portion of the animal economy, we are naturally led, therefore, in reviewing the mus cular system generally, to take this great phy siological axiom as our guide, and beginning with the simplest forms of life to trace the first appearances and successive complication of the motor organs as we advance through the. different classes of animated beings.
In the Cuvierian classification of the Itbgne Animal all the lower animals, originally con founded under the general name of Zoophytes, are included in one great division, called Rapiers, from the circumstance that many forms of these animals exhibit more or less of a radiated arrangement in the general malice of their bodies. For the term ItAD1ATA, in the article ANIMAL KINGDOM of this Cyclo paidia, Dr. Grant has substituted that of " acknowledging, at the same time, that the name selected by him was of equally partial application, and conse quently unsatisfactory ; inasmuch as, in the great majority of the animals ranged under it, so far from any nerves being visible, " disposed in a circular manner around the oral extremity of the body," not a trace or vestige of nervous fibre is by any means discoverable ; and, moreover, many of the animals thus grouped under one denomination are so remote and dissimilar from each other in every feature of their economy, that it is impossible to regard them even as being organized according to the same type. As regards the condition of their muscular system, the most striking differences are at once perceptible ; the Sponges, the Polyps properly so called,' the Fopygastrieo, and the Acalephe, have the texture of their bodies so soft and gelatinous, that not a mus cular fibre is by any means apparent in any of them ; while, on the other hand; the Echino derms have muscular systems constructed upon exceedingly elaborate and complex Taking the nervous system for our guide, it is at once evident that the presence of nerves and of muscles goes hand in hand, and the ItADIATA of Cuvier or the CYCLONEUR4 of Grant is at once separable into two great groups, one divi sion being without either visible nerves or mus cles, while the other is found to possess both. Classifying them, therefore, according to this principle, and adding to the list of radiated animals some which, in the article ANIMAL KINGDOM, have, as we think, been erroneously included in the Diploneurose (articulated) sub kingdom, they readily range themselves under the following denominations :— Acn IrA.
Animals with neithrr nerves nor musclesi Agastrica.
Polypi ph era. Polygastrica. Acalephm.
Sterehnintlia.