CHAPTER III 



THE ELEMENTS OF STRUCTURE 



(Morphology) 



Animals may be studied alive or dead, in regard to their 

 activities or in regard to their parts. We may ask how they 

 Hve, or what they are made of ; we may investigate their 

 functions or their structure. The study of hfe, activity, 

 function, is physiology ; the study of parts, architecture, 

 structure, is morphology. 



The first task of the morphologist is to describe structure 

 (descriptive anatomy) ; the second is to compare the parts 

 of one animal with those of another (comparative anatomy) ; 

 the third is to try to state the " principles of morphology," 

 or the laws of vital architecture. 



But just as the physiologist investigates life or activity at 

 different levels, passing from his study, of the animal as a 

 unity with certain habits, to consider it as an engine of 

 organs, a web of tissues, a city of cells, and a whirlpool of 

 living matter ; so the morphologist has to investigate the 

 form of the whole animal, then in succession its organs, 

 their component tissues, their component cells, and finally, 

 the structure of protoplasm itself. The tasks of morphology 

 and of physiology are parallel. 



Morphology thus includes not only the description of ex- 

 ternal form, not only the anatomy of organs, but also that 

 minute anatomy of tissues and cells and protoplasm which 

 we call histology. Moreover, there is no real diff"erence 

 between studying fossil animals which died and were buried 

 countless years ago, and dissecting a modern frog. The 

 anatomical palaeontologist is also a student of morphology. 



Finally, as the greater part of embryology consists in study- 



40 



