INTRODUCTION. xi 



respecting them. If the nervous system be taken as the foundation, there is tolerably 

 distinct subdivision; but it is an internal one, often not very easily ascertained, and still more 

 generally hidden from popular observations, so that it is of little use to common readers. 



The first of these subdivisions has what may be considered, perhaps, as the principal brain 

 in the form of a sort of collar surrounding the gullet. From this collar nervous filaments 

 proceed, which thicken into knots or ganglions in the course of their length, and the animals 

 which have them have thence been denoted GANGLIATA, or ganglionic animals; but the 

 term does not carry much information. Of these ganglioned animals there is another division, 

 which, if the structure of the nervous system is to be taken as the foundation of arrangement, 

 is of considerable importance ; namely, that of those which have something analogous to a 

 spinal cord, though not supported by a spinal column, unless we are to consider the external 

 covering which invests the whole body as having that character, and those which have the 

 nervous filaments diffused from the originating collar in such form that no one of them 

 predominates very much over the rest. The first of these have the principal nervous elon- 

 gation in the form of a cord, extending longitudinally backwards, and enlarged into a greater 

 or smaller number of knots or ganglions ; and as the body is often formed into joints or 

 segments, having some slight resemblance to rings, these have been called ANNELIDES, or 

 ringed animals. There are so many diversities of appearance, habit, and the structures 

 of the other systems, that no very precise or satisfactory information can be grounded 

 upon these characters. There are, however, some external characters accompanying this 

 knotted nervous cord. The animals have a head, though, in the common meaning of the 

 word, a brainless one ; and they have detached or articulated feet, or some sort of substitutes for 

 them. They have also, in some instances, internal cartilaginous substitutes for bones ; their 

 external hard coverings, when they have them, are intermediate in their com position bet ween 

 bones and shells; and they have at least some of the organs of sensation belonging to 

 the vertebrated animals, or at least bearing some analogy to them. They have also this 

 farther in common with the vertebrated animals, that if their bodies are supposed to be divided 

 vertically by a mesial plane passing from the anterior to the posterior extremity, the external 

 parts are symmetrical, that is, the one half corresponds with the other, only the one is turned 

 to the right, and the other to the left. Those animals are, therefore, to be considered as 

 making nearer approximations to the vertebrated animals in some of their characters, both 

 external and internal, than any others of the invertebrated ones. 



The second subdivision of gangliated animals have no resemblance to the vertebrated 

 animals in their structure ; and they vary so much from each other, that no very precise 

 general account of them can be given. They are termed MOLL use A, or soft-bodied animals, 

 from the circumstance of none of them having any internal bones, though many of them have 

 shells which entirely cover them, and others have portions of shell, more or less produced, 

 concealed under the skin or in its folds or duplicatures. 



The second principal division of invertebrated animals have been called RADIATA, or 

 rayed animals; because many of them, in some part of their structure at least, have a 

 radiated form something resembling the rays of a star. That does not, however, so well 

 point out the nature of the nervous system as the epithet gangliata, in the former division ; 

 because in many of them it is difficult to trace the nervous ramifications to any definite centre. 



THE VEGETABLE KINGDOM. 



VEGETABLES, like animals, do not admit of general definition. The' name signifies 

 " that which grows;" but though growth is common to all vegetables, it is also common to 

 all animals ; and there are some minerals that have a sort of growth. Diamonds, for 

 instance, are tolerably well ascertained to grow in some soils, and rock crystals on some 



