3<D THE PXOTOZOA 



weight, that since organized living bodies are composed of the same 

 materials as unorganized or lifeless bodies, and after death are again 

 resolved into those same lifeless materials, it may be logically assumed 

 that in the beginning and under certain conditions, simple materials 

 were combined into new compounds having the properties which we 

 know to-day as life. Haeckel at first held that these complex com- 

 pounds were primitive organisms which he called Monera or organisms 

 consisting of homogeneous plasm without differentiations of any kind, 

 since differentiation follows the localization of function and can 

 originate only as a result of living activity. In his later work, how- 

 ever, Haeckel ('96) follows Nageli in postulating simple structural 

 units as the primitive forms of life instead of the homogeneous and 

 formless lumps of proteid. 



Nageli maintained that two stages must be distinguished between 

 inorganic matter and the lowest organisms known to us. The first 

 consisted of the synthesis of the albumin compounds and the organi- 

 zation of these into micellae which constitute primordial plasm. 

 The second stage was the transformation of the primordial plasm 

 into the simplest of living organisms. Haeckel's hypothetical Monera, 

 if they existed, would approach most closely to these primordial 

 forms of living matter, being described as " organisms without 

 organs." They could be called structureless, however, only from the 

 anatomical standpoint. Physically, the earliest organisms must have 

 been already complex, for, chemically considered, an albumin mole- 

 cule is an extremely complex substance, and every unit of plasm 

 which Nageli calls a micella must have had, and now has, that same 

 complex composition. 



Somewhere in the obscurity of this early period came the change 

 from the plant to the animal mode of nutrition. The latter must 

 have begun at an early time, although the possibility of change at 

 any time from plant to animal nutrition is not excluded, as shown by 

 the numerous instances among the higher plants of adaptation to a 

 parasitic or a saprophytic mode of life. So too, among the Protozoa, 

 the acquisition of a cannibalistic mode of life, or, as Haeckel calls it, 

 metasitism, may have required, and probably did require, a long 

 period, and there is little reason to doubt Haeckel's view that the Pro- 

 tozoa are polyphyletic in their origin. We possess no positive data 

 for the conclusion as to which of the Protozoa were the most primi- 

 tive. In considering this question, it must not be overlooked that, 

 during the eras that have passed, the Protozoa may have been 

 adapted and re-adapted many times over to changing conditions of 

 environment, and living species have, in all probability, not come 

 unchanged from that remote past. 1 



1 See Lankester ('91), Klebs ('92), and infra, p. 99. 



