CHAPTER XII. 

 3I0RPH0L0GY OF ORGANS. 



In the foregoing pages the structure of a number of types of 

 animals has been considered, and the development of one 

 form has been dealt with. It may be useful to extract from 

 that survey (adding something to the extract on the way) an 

 account of the main facts in the structure of the higher animals 

 from the point of view of the several organs and systems of 

 organs. Hitherto we have characterized different animals by 

 the structure of their different parts. We shall now examine 

 seriatim the various organs themselves. The facts of Zoology, 

 when treated in this way, are often spoken of as comparative 

 anatomy or morphology. The term " Zoology ' may be usefully 

 retained for the consideration of animals in their entirety, their 

 anatomy, mode of life, classification, and history, as indicated 

 by fossil remains. The zoologist deals with the animal as an 

 unit; the comparative anatomist with the organ. It is not 

 intended, however, to insist upon any sharp line of division 

 between these two aspects of the zoological side of biology; 

 they obviously overlap. 



In investigating the modifications of organs and systems of 

 organs through the animal series, it is clearly requisite to be 

 assured as to the exact equivalence of the organs under 

 consideration. And this necessitates the use of terms with 

 a definite meaning, such as is not always afforded by words in 

 common use. It is not pedantic to speak of the jaws of an 

 insect as mouth appendages. To term them "jaws" is to 

 imply something in common with the jaws of a tiger. There 

 is absolutely nothing in common structurally between the two 



