15 



But of all the characteristics which have been employed in estabteih- 

 ing the limits of animal and vegetable nature, there is one quite sufficient 

 to distinguish these two great classes of beings, but which has not been 

 allowed the weight it deserves. 



The zoophyte, which, fixed to a rocky habitation, cfcnnot change its 

 place, is confined to partial movements, that certain plJnts possess, and 

 besides, has not that sensitive unity, so remarked in man, and in the ani- 

 mals who nearest resemble him in their organization: the zoophyte, 

 whose name indicates an animal-plant, is totally separated from all be- 

 ings of the vegetable kingdom, by the existence of a cavity, in which ali- 

 mentary digestion is carried on, a cavity by the surface of which is effected 

 an absorption, an imbibition, far more active than that which takes place by 

 the external surface of the body. From this shapeless animal, up to raan ? 

 nutrition is effected by two surfaces, and especially the internal, whilst 

 in the plant, nutrition, or rather the absorption of nutritive principles, is 

 only by the external surface*. 



Every animal may be considered, in extreme abstraction, as a nutritive 

 tube, open at the extremities!; the whole existence of the polypus seems 

 reduced to the act of nutrition, as its whole substance is employed in the 

 formation of an alimentary tube, of which the soft parietes, extremely 

 sensible and contractile, are busied in appropriating to themselves, by a 

 sort of absorption, the substances which are brought into it. From the 

 worm up to man, the alimentary canal is a long tube, open at the extre- 

 mities; at first, only of the length of the body of the animal, not bent at 

 all in passing from the head to the tail, and carried on towards the mouth, 

 and towards the anus, with the external covering of the body, but soon 

 returning upon itself, and stretching out into length, far beyond that of 

 the body which contains it. 



It is in the thickness of the pari0tes of this animated tube, betwixt the 

 mucous membrane that lines it inwardly, and the skin with which this 

 membrane is continuous, that all the organs are placed, which serve for 

 the transmission and elaboration of fluids, together with the nerves, the 

 muscles, in short, all that serves for the carrying on of life. As we rise, 

 from the white-blooded animals, to the red and cold-blooded, from these 

 to the warm-blooded, and irom these to man, we see a progressive multi- 

 plication of the organs that are contained within the thickness of the pa- 

 rietes of the canal: If we follow, on the other hand, the descending scale, 

 v/e see this structure gradually simplified, till we arrive at last at the 

 polypus, and find in it only the essential part of animal existence. The 

 simplicity of its organization is such, that it may be turned inside out, 

 and the external be made the internal surface; the phenomena of nutri- 

 tion, which are the whole life of the animal, go on, from the close ana- 

 logy between the two surfaces; unlike to man and the greater part of 

 animals, in whom the skin and the mucous membranes, though growing 

 into e4k.h other, though linked by close sympathies, are far from possess- 



* This most prominent characteristic of animal organization was lirst pointed out by 

 Boerhaave, anu afterwards insisted on by Dr. Alston of Edinburgh, and recently by Mr. 

 A. T. Thomson, in his excellent work on the Elements of Botanv. Copland. 



f Lacepzde, Histoire Naturelle des Poissons, torn 1. There may be brought against 

 ibis principle, the instance of some zoophytes, such as sponges, &c.; but do these bo- 

 dies really belong to the animal kingdom ? and should not we be warranted in rejecting 1 

 them, by the want of the alimentary cavity, the essential characteristic of animal exist- 

 in ce ? Author's Jiote- 



