16 THE NEWEST THEORIES CONCERNING EVOLUTION SEC. 



primitive time . . . Among known living beings there are 

 none which could have arisen by abiogenesis " the lowest 

 living plants have already a cell-membrane and the Monera 

 cannot live independently, i.e. without the products of 

 decomposition of other organisms, as must be the case with 

 organisms produced by spontaneous generation. " The beings 

 which are capable of arising by a spontaneous origin are there- 

 fore not yet known to us. They must have a still simpler struc- 

 ture than the lowest organisms which the microscope shows us" 

 they may be " beneath the lowest size which is visible with 

 the microscope." The organic being due to spontaneous genera- 

 tion can be but a minute drop of homogeneous plasma " which 

 consists of albuminates without admixture of other organic 

 compounds than food materials, without external form and 

 without distinction of parts, and which grows and feeds on 

 the inorganic or simple organic compounds from which itself 

 arose." " Abiogenesis thus presupposes a spontaneous forma- 

 tion of albuminates." Probably the spontaneous albumen 

 production takes place still at the present time " in the moist 

 superficial layer of some porous material (loam, sand), where 

 the molecular forces of solid, liquid, and gaseous bodies are at 

 work together," favoured by a definite degree of warmth, " so 

 that it may still take place in warmer climates as well as in 

 the warmer part of the year in colder regions." 



Nageli advocates with Weismann the view that external 

 influences that, in particular, climatic conditions and changes 

 of nutrition have no effect on the transformation of species. 

 He supports his argument with experiments which he made 

 upon plants ; placing them under such changed conditions 

 and finding that these had no relation whatever to the appear- 

 ance of varieties. 1 



1 C. Nageli, Ueber den Einfluss der aussern Verhaltnisse auf die Varietaten- 

 bildung im Pftanzenreiche. Sitzuugsb. d. math.-phys. Klasse d. k. bayer. Akad. 

 d. Wissensch. zu Miinchen, 18th November 1865 ; and Das gesellschafiliche 

 Entstehen neuer Species, ibid. 1st February 1873. 



