HIGH SCHOOL ZOOLOGY. 261 



CHAPTER X. 



General Principles. 



1 . In the preceding Chapters the principal forms of Animal 

 Life have been reviewed, a particular standpoint having, been 

 selected in each of the chief subdivisions of the Animal King- 

 dom. An accessible and, where possible, a primitive type has 

 been somewhat carefully examined, and the modifications of form 

 then traced throughout the sub-kingdom or class to which it 

 belonors. The examination has been confined to the more ob- 

 vious characters of the adult organism, but occasional references 

 have been made to minute structure, and to the developmental 

 stages through which the adult form is reached. It has been 

 made apparent that zoologists classify animals according to the 

 degree of resemblance which they exhibit in these respects, and 

 that, therefore, classification is a Synopsis of the results of such 

 structural studies. 



2. While it has been chiefly with this — the morphological — 

 aspect of Zoology that we have hitherto been dealing, other 

 topics have been incidentally touched upon. It has been made 

 evident that there is the closest relation between the form of 

 organs,'and the uses to which they are put (whatever may be 

 the explanation of this relation), that the various kinds of ani- 

 mals are limited to certain parts of the earth's surface, that the 

 forrms of life at present on the earth are diffei-ent from those 

 which occupied it in past times, and that there is the closest 

 connection between animals and their suri-oundings. The 

 present chapter will be reserved for a more systematic discus- 

 sion of such topics as these, and an endeavour will be made to 



