THE BIOLOGICAL SCIENCES. 9 



scientific study of every phenomenon has for its ultimate object 

 the discovery of its cause. ^Etiology is therefore inseparable 

 from any of the several branches of biology and cannot properly 

 be assigned an independent place. 



Psychology and Sociology are not yet generally admitted to 

 constitute branches of biology, and it is customary and con- 

 venient to set them apart from it. The progress of these sci- 

 ences has clearly shown, however, that their study is inseparable 

 from that of biology in the ordinary sense. 



It will be observed in the scheme that morphology and physi- 

 ology overlap ; that is, there are certain biological sciences in 

 which the study of structure and of action cannot be separated. 

 This is especially true of embryology, which considers the suc- 

 cessive stages of embryonic structure and also the modes of 

 action by which they are produced. And finally it must not be 

 forgotten that any particular arrangement of the biological sci- 

 ences must be in the main a matter of convenience only; for it is 

 impossible to study any one order of phenomena in complete iso- 

 lation from all others. 



