92 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



kind of outside pressure, the so-called tissue tension, may 

 account for the arrangement in surfaces minimae areae. 

 Cleavage stages are perhaps the very best type in which 

 our physical law is expressed : and here it may be said 

 to have quite a simple application whenever all of the 

 blastomeres are of the same physical kind, whilst some 

 complications appear in germs with a specialised organisa- 

 tion and, therefore, with differences in the protoplasm of 

 their single blastomeres. In such instances we may say 

 that the physical law holds as far as the conditions of the 

 system permit, these conditions ordinarily consisting in a 

 sort of non-homogeneity of the surfaces. 



It seems, from the researches of Dreyer, 1 that the forma- 

 tion of organic skeletons may also be governed by the 

 physically conditioned arrangement of protoplasmatic or 

 cellular elements, and some phenomena of migration and 

 rearrangement among cleavage cells, as described by Koux, 

 probably also belong here. 



But let us never forget that the laws of surface tension 

 only give us the most general type of an arrangement of 

 elements in all these cases, nothing else. A physical law 

 never accounts for the Specific ! Capillarity gives us not 

 the least clue to it. As the organic substance, at least in 

 many cases, is a fluid, it must of course follow the general 

 laws of hydrostatics and hydrodynamics, but life itself is as 

 little touched by its fluid-like or foam-like properties as it 

 is by the fact that living bodies have a certain weight and 

 mass. 



All indeed that has been described may be said to 

 belong, in the broadest meaning of the word, to what is 



1 Jena. Zeitschr. 26, 1892. 



