ON THE BRITISH ANNELIDA. 269 



ception of the mechanism oflight in these animals ; if this endowment really is 

 conferred upon them., under the conditions and in conformity with the laws 

 which affect these organs in all the higher animals. It were however by no 

 means irreconcileable with the views entertained at present as probable by 

 many philosophers with reference to the properties of light, to suppose that 

 this subtile agent may be rendered perceptible to the sensorium of the hum- 

 blest animals, by means of a mechanism very different from that which aria- 

 tomists and opticians recognize in the apparatus of an eye. It is not essential 

 to the practical purposes of the lowest forms of life that the objects of the 

 external world should be seen, that pictures of them should be painted upon 

 the retina ; it were enough that the mere presence or absence of an objective 

 body should become evident to the sensations of the animal by the positive- 

 ness or negativeness of the impressions received. A refinedly exalted sense of 

 touch, tactile sensibility, would suffice to accomplish this object. It is not 

 easy for those who have never enjoyed the spectacle of the ' feat of touch,' 

 performed by the tentaculated worms, to estimate adequately the extreme 

 acuteness of the sensibility which resides at the extremities of the living and 

 sagacious threads with which tiie head and sides of the body are garnished. 

 They select, reject, move towards and recede from minute external objects 

 with all the precision of microscopic animals gifted with the surest eagle- 

 sight. The necessity therefore of ordinary organs of sight, in the present 

 state of physical and physiological science, it is by no means essential to 

 admit, while acknowledging that under agency and stimulus of light the 

 humblest beings, though unendowed with normal visual organs, may yet 

 steer themselves harmlessly, readily and unerringly through the thickly- 

 tangled labyrinth of mud and stone and gravel and weed, amid the twilight 

 of which the habitat of many of them may have been cast. 



It is a remarkable fact in the history of the Annelida, that scarcely any 

 species, however organized, whether furnished or not with external locomo- 

 tive organs, in its numerous and varied muscular evolutions ever moves 

 directly backwards. The movements consist always of serpeiitiform pranks, 

 or those of elaborate coiling. It is by the head however that the movement 

 is invariably initiated. The tail is always in the rear, never in the van. The 

 animal never marches backwards. The head never delegates to the tail the 

 authority of leading, directing or controlling the evolutions of the frame; 

 not even in the Clymenidm, in which the caudal ganglion exceeds the ce- 

 phalic in dimensions. The power of retreat however, by exception, does 

 exist in the tubicolous worms, and they are ingeniously provided with loco- 

 motive appendages by which the back-movement is performed with as much 

 facility as the forward. These curious facts are well calculated to elucidate 

 many points of great interest in the physiology of the nervous system of these 

 annulose forms. The elaborate dissections of Mr. Newport have already 

 proved beyond doubt that fibres of communication, from every part of the 

 body of the articulated animal, converge upon, while others radiate from, the 

 central cephalic ganglia. Through the intervention of such cords, these 

 masses become the controllers of all the consensual muscular actions of the 

 body. As Dr. Carpenter has argued with masterly clearness, sensation, the 

 rousing of consciousness, is involved in such movements. Although excited 

 by external impressions, they are not automatic — they are raised in character 

 one degree above the purely automatic. Although stimulated by influences 

 from without, the cephalic ganglia, unlike the abdominal, yet possess the 

 power of subordinating and coordinating a complex succession of muscular 

 evolutions with a view to the attainment of a definite end. This is instinct I 

 This regulating power does not however reside, even in its lowest form, in the 



