98 THE THEOBY OF EVOLUTION 



relations/ It signifies also, even, according to Hertwig 

 and the same may be said of other naturalists who come 

 here into consideration 1 that it is not merely by the 

 existence of a definite physical aggregate condition, or 

 by a stiff internally connected mechanism, as is the 

 case in a machine, or by peculiar chemical combinations, 

 that life can be explained. That the phenomena of 

 life can be referred to the properties of the liquid aggre- 

 gate condition 0. Hertwig denies ' emphatically ' and 

 refers in that connection to many other investigators. 2 

 The ' structures/ however, also explain nothing, since 

 all the coarser structures observed in cells tissues, 

 threads, network structures, and seed structures- 

 have shown themselves long since to be temporary 

 forms, conditions of the protoplasm, or the morpho- 

 logical expression of a particular function. They can 



1 Even Prenant, the author of the first section of vol. i. of the Traite 

 d* Histologie, can only classify the combinations of matter which take place 

 in protoplasm according to their purpose and their vital importance. He 

 defines six groups foodstuff, reserve and excreted products, and rigorously 

 specialized instruments, e.g. myelin, chlorophyll, haemoglobin supporting 

 material and active material. Not a word of chemico-physical points of 

 view which, for instance, arise in connection with aggregate conditions or 

 definite molecular groups. He introduces this grouping by the words : 

 ' On peut cependant [since ' chemical ' is not concerned], etablir une classifi- 

 cation biologique parmi les differentes substances trouvees dans les cellules ' 

 (see p. 10). See also particularly E. B. Wilson : The Cell in Develop- 

 ment and Inheritance, New York, 1900, p. 316. This work is certainly the 

 best that has been written on general biology. Furthermore, O. Hertwig : 

 Allg. Biologie, p. 26 ; E. Wasmann : Moderne Biologie, chap. iii. 



2 Allgemeine Biologie, p. 16 : ' With Naegeli and many other investigators 

 we share the conviction that the complicated phenomena of the vital 

 processes before all, those of inheritance are not explicable by the 

 qualities of liquids or matter in solution. Wiesner is justified, therefore, in 

 terming the attempt to refer the peculiarities of the living substance to 

 qualities of liquids a surprising one.' 



