158 SEA-SIDE STUDIES. 



reproduction. Such a state of things is presented by the 

 Actinia/'* Wliat is here said respecting Respiration is veiy 

 questionable, but the general idea of an increasing specialisa- 

 tion of function, in the increasing separation of the parts, 

 is well expressed. It is indeed a fundamental law that 

 every advance in complexity of organisation takes place 

 through a gradual differentiation, or specialisation, of the 

 general envelope. These important synonyms, differentia- 

 tion and specialisation, I will explain by illustrating the 

 law to which they point, namely, the law of animal develop- 

 ment first enunciated by Goethe, and strikingly applied by 

 Von Baer f : — Development is always from the General to 

 the Particular, from the Homogeneous to the Heterogeneous, 

 from the Simple to the Complex ; and this hy a gradual 

 series of differentiations. 



When we say an organ has been formed out of a tissue, 

 we say a differentiation has taken place ; and the function, 

 e. g. respiration, which before was performed by the general 

 tissue, is now specialised, i. e. performed by that special 

 organ. A homogeneous mass of organic matter, such as the 

 Amoeba, which has no organ whatever, performs all the 

 functions of Assimilation, Respiration, Locomotion, and Re- 

 production, by its general mass, not by any special organs. 



The process of differentiation by which special organs are 

 gradually developed in the ascending scale of the animal 

 series, is equally exhibited in any particular case of develop- 



♦ Draper : Jlunuin rhysiology, 1856, p. 501. 



t Goethe : Werke xxxvi., Zur Morphologie, 1807. VoN Baer : Zur Ent- 

 wkkelunysyeschichte. 1828. I. 153. 



