532 



MUSCULAR SYSTEM, 



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 modern Zoologists all admit, 

 that the nervous system, whatever may be Us 

 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 Regne 

 Animal all the lower animals, originally con- 

 founded under the general name of Zoophytes, 

 are included in one great division, called 

 RADIATA, from the circumstance that many 

 forms of these animals exhibit more or less of 

 a radiated arrangement in the general outline 

 of their bodies. For the term RADIATA, in 

 the article ANIMAL KINGDOM of this Cyclo- 

 paedia, Dr. Grant has substituted that of 

 " CYCLONEURA, " 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 Polygastrica, 

 and the Acalephee, have the texture of their 

 bodies so soft and gelatinous, that not a mus- 



* In the article referred to, polypiform animals, 

 with ciliated tentacula around the mouth, are 

 classed with the Polypifera. Recent observations 

 made by Lister, Milne Edwards, Ehrenberg, and 

 Dr. Arthur Farre, have, however, since shewn such 

 creatures to be so far removed iu their general 

 organization from the true Poljps, that they now 

 constitute a distinct class under the title of Bryoxoa. 



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 principles. 

 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 RADIATA 

 of Cuvier or the CYCLONEURA 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 : 



Ac RITA. 



Animals with neither nerves nor muscles. 

 Agastrica. 

 Polypiphera. 

 Polygastrica. 

 Acalephse. 

 Sterelmintha. 



NEMATONEURA Animals possessed both 

 of nerves and muscles, either without percep- 

 tible ganglionic centres of innervation, or where 

 these do exist, they are extremely rudimentary, 

 and not arranged in any parallel series. This 

 division will include 



Ccelelmintha, 



Bryozoa, 



Rotifera, 



Epizoa, 



Echinodermata. 



The term Agastrica is here proposed to in- 

 clude those lowest forms of animal existence 

 which obviously form the transition from the 

 Vegetable to the Animal Kingdom ; many of 

 them indeed seeming rather to belong to the 

 former than to the latter division of the orga- 

 nized world. Such are, for example, the con- 

 fervoid animalcules, which, in their structure 

 and mode of reproduction, are evidently nearly 

 allied to vegetables, although from the seem- 

 ingly spontaneous movements of which some, 

 the Oscillatoriae, &c. are capable, they have been 

 claimed by Zoologists as belonging to their de- 

 partment. The Sponges ( Porifera, Grant) are 

 equally allied to vegetables in the nature of the 

 living parenchyma that invests and forms their 

 porous or reticulated skeletons; and most inti- 

 mately related to these,notwithstanding the diffe- 

 rent texture of their framework, are many of the 

 lithophytous Corallines and Fungi^e, the solid 

 portions of their skeleton being in like manner 

 deposited in an organized soft tissue, the animal 

 nature of which is by no meansas yet clearlyesta- 

 blished. All the above plant-like forms agree, 

 however, in one grand and striking circum- 

 stance, they are devoid of any stomachal or 

 digestive cavity, a feature of their economy 

 which of itself would be sufficient to raise a 

 doubt whether they are strictly entitled to be 

 regarded as animals or classed with the vegeta- 

 ble creation. 



