An Introduction to Zoology. 37 



arranged circularly, to represent circular muscles ; and every various com- 

 bination of the muscular fibres which takes place in nature, might be 

 equally exhibited; and models might be constructed which would imitate by 

 electricity every variety of muscular action — the experiment would be easy 

 and highly illustrative : for the power conveyed by the nerves to the 

 muscles is clearly a power inducing a natural repulsion of their fibres, and 

 many reasons may lead us to believe that it is very nearly connected with 

 those electro-galvanic forces, which, as every one knows, furnish such 

 ^^olent stimuli to muscular action. 



In the very lowest animals, such as the polypi and medusae, (jelly 

 fish) we do not see distinct fibres, but only a uniform gelatinous sub- 

 stance 5 here, however, we still observe contractility, and consequent 

 motion of the parts — how is this produced? Must we not conceive that 

 the minute internal structure of this gelatinous mass is really cellular, and 

 that the cellulse are arranged in linear series, and in their relaxed state 

 elongated. Repulsive powers, communicated to such a texture, would 

 naturally convert each cellule from an elongated ovoid into a spherical 

 form, and thus necessarily shorten each linear series of those cellules. This 

 view, indeed, has, we believe, never been taken by previous writers, and 

 we therefore offer it with diffidence, as a mere suggestion. The difficulty, 

 however, of which this solution is submitted, belongs only to an almost 

 insensible fraction of the animal kingdom, for the distinct fibrous structure 

 is already manifest in the actiniae, a race scarcely distinguishable from the 

 polypi, and it pervades all the orders above this very low point : hence- 

 forth, therefore, the mode of action becomes simply mechanical, and perfectly 

 obvious. 



The power being thus obtained, its application is principally varied 

 according as the animals possess any solid frame work, which may afford 

 on the one hand firm points of support for the attachment of the muscular 

 fibres, and fulcra, or originating points, to which this action is to be 

 referred ; and on the other, levers on which that action is exercised ; or, 

 as those animals are entirely composed of a soft and pulpy mass. In 

 the latter case, however, the muscles, by proceeding in a radiating form, 

 from a common central point, or being disposed in a circular arrangement, 

 may produce considerable varieties in the conformation of the parts and 

 motions resulting, but far less than when the solid parts of attachment are 

 present,* Such points are afforded in the bivalve shell fish by their 



• The means of locomotion thus afforded, are as various as the wants of the dif- 

 ferent animals, and manifest tlie marvellous riches of creative design, in producing 

 the same great ends by such a diversity of means. Some animals, species of zoo- 

 phytes and bivalves, for instance, do not require any change of place, but are suffi- 

 ciently supplied by the prey which the element wafts within reach of their mouths or 

 tentacula ; these remain fixed. Others have a projecting muscular organ, more like 

 a tongue in its structure, though called from its use a foot ; by contracting and 

 dilating this organ, they draw or push themselves along. Some bivalves (the scallop) 



