150 MEAXIXG OF THE SYSTEM. 



The undifferentiated contractile substance, sarcode or protoplasm^ 

 was probably the starting-point of all organic life. 



If these suppositions are correct, species no longer retain the signifi- 

 cation of independent and immutable units, and appear, according to 

 the great law of evolution, only as transient groups of forms, capable 

 of change, and confined to longer or shorter periods of time, to definite 

 conditions of life, and preserving, as long as these conditions do not 

 vary, a constancy in their essential characters. The different categories 

 of the system show the closer or more remote degree of relationship ; 

 and the system is the expression of genealogical relationship founded 

 upon descent. All systems, however, must be imperfect and full of 

 gaps, since the extinct ancestors of organisms living at the present 

 time can only be very imperfectly supplied by the geological record ; 

 numerous intermediate forms are wanting and finally no traces of 

 organic remains from the most ancient periods are preserved. 



Only the ultimate twigs of the enormously ramified ancestral tree 

 are accessible to us in sufficient number. Only the extreme points 

 of the twigs are completely preserved ; while of the numerous rami- 

 fications of the branches only the existence of a stump here and 

 there has been demonstrated. Hence it appears quite impossible, in 

 the present state of our knowledge, to attain to a sufficiently sure 

 representation of this natural genealogical tree of organisms ; ?nd 

 while we admire the bold speculations of E. Haeckel's genealogical 

 attempts, it must be admitted that at present there is room for 

 innumerable possibilities in detail, and that subjective judgment 

 holds a more conspicuous place than objective certainty of fact. 

 Hence we must be contented for the present with an incomplete 

 and more or less artificial arrangement ; although the conception of 

 the natural system theoretically is established. 



When the fundamental arguments -of the Darwinian theory of 

 selection and the transmutation theory founded upon it are submitted 

 to criticism, it is soon apparent that direct proof by investigation 

 is now, and perhaps always will be, impossible; for the theory is 

 founded upon postulates which cannot be submitted to direct inquiry. 

 Periods of time which cannot be brought within the limits of human 

 observation are required for the alteration of forms under natural 

 conditions of life ; and the extremely complicated interactions, which 

 in the natural state under the form of natural selection are tending 

 to change plants and animals, can only be grasped in a general sense, 

 while in their details they are practically unknown to us. 



Further, plants and animals which are under the influence of 



