GENERAL ANATOMY. 69 



opposite course from that which anatomy actually takes, 

 for this resolves the animal body into its elementary parts, 

 its organs, tissues, and cells. 



Instead of analytical we will pursue synthetic anatomy. 



The synthesis of an organism, of which in General 

 Anatomy we can only gain an idea, actually takes place in 

 nature during the development of every animal. Embryo- 

 logically every organism is at some time a simple element, 

 a cell ; this cell divides and gives rise to tissues ; from the 

 tissues are formed organs, and from the organs the regularly 

 membered whole of the animal body is combined. If the 

 general ontogeny proceeds synthetically, it then agrees in 

 its manifestations with the processes which go on in nature 

 and which are accessible to direct observation. 



GENERAL ANATOMY. 



The Morphological Units. The expression " con- 

 stituent parts of the animal body " can be used in a double 

 sense. We can speak of the chemical units, the chemical 

 combinations, which form the tissues ; these are the sub- 

 ject of animal chemistry, and may therefore be passed 

 over here. But we may also speak of the constituent units 

 (morphological units) of the animal body ; these are the 

 cells. * These and their transformation into tissues, organs, 

 and entire animals are for us of vastly greater importance. 



I. THE MORPHOLOGICAL UNITS OF THE ANIMAL BODY. 



The Cell. The study of the morphological units of 

 the organic body first found a firm foundation in the cell 

 theory. Every scientific animal and plant Anatomy must 

 therefore take as its starting-point the study of the cell. 



*The cell is not the ultimate unit of structure. All organisms digest, 

 assimilate, excrete, and reproduce. In the higher organisms each of these 

 functions is carried on by groups of cells, but in the unicellular forms all the 

 functions are performed by the single cell; hence there must be in the latter 

 certain units of a lower grade, i.e., molecules set apart for special func- 

 tions. The cell, then, is to be regarded as equal to a complex molecule or 

 group of molecules. ED. 



