CHAPTER I 



CLASSIFICATION— STRUCTURE OF MAN TAKEN AS 



A TYPE 



GENERAL CONSIDERATIONS 



In considering any scheme of classification, and in subsequently 

 dealing with the various functions of animals, reference will con- 

 stantly have to be made to external characters and to various sets 

 of organs and their mode of action. It would therefore appear 

 desirable, in order to clear the ground, to give some account of 

 certain points of fundamental importance, and this can perhaps 

 best be done by fixing our attention at start upon some familiar 

 organism. It is undoubtedly the best plan to begin with the 

 known, and from this to proceed to matters regarding which the 

 majority of readers are more or less ignorant, though throughout 

 this book no technical knowledge will be assumed. And for 

 various reasons, such, e.g., as that a very large number of persons 

 have some elementary acquaintance with Human Anatomy and 

 Physiology, it is deemed advisable to begin this chapter by a brief 

 account of the structure and life-functions of man himself. 



Symmetry. — The body of a human being, and the same is 

 true for the common domestic animals, is built with a certain 

 sort of regularity to which the name of two-sided or bilateral 

 symmetry is applied. And to fully appreciate what is meant by 

 this we must suppose the body to be placed with its 

 front surface downwards, as is permanently the case 

 in a dog, rabbit, or frog. This is clearly necessary, 

 for if we are to compare man with the lower animals 

 the same relative positions must be assumed for 

 purposes of description. 



Bilateral symmetry means, then, that the body can be divided 

 into two corresponding halves in one way and one way only. 

 Simple examples of this kind of regularity are afforded by an 

 isosceles (or equal-sided) triangle, many leaves, and most of the 



