353 ] 



XIII. 



VARIATION : GEEMINAL AND ENVIRONMENTAL. 



By J. C. EWART, M.D., F.R.S. 

 Regius Professor of Natural History in the University of Edinburgh. 



[Communicated by Professor D. .J. Cunningham, M.D., F.R.S. , Vice-President, Roy. Dublin Society.] 



(Read March 20, 1901.) 



Introductory. 



All are agreed that variability is intimately associated with clianges in the 

 pi'otoplasm out of which animals and plants are made, but there is not yet 

 universal agreement as to the causes of these changes. It may, however, be 

 taken for granted that protoplasm has varied to produce recent and extinct 

 organisms, either (1) because it was at the outset endowed with inherent internal 

 attributes, or (2) because it has from the first been susceptible to the influence of 

 external forces. 



A century and a half ago certain naturalists (the extreme " pref ormationists " 

 or "evolutionists") believed in the theory of encasement, or emboitement, which 

 not only implied that each ovum contained a complete fully formed embryo, 

 but that each embryo contained ova for the next generation, these ova, other 

 ova in their turn, and so on ad infinitum — Eve, for example, "encasing" all her 

 descendants, each complete but necessarily infinitely minute. 



The " pref ormationists " of the middle of last century — for a time championed 

 by Bonnet — may be said to be now represented by neo-preformationists with 

 Nageli as their most scientific apologist. The main difference between the extreme 

 old and extreme new "evolutionists" is, that the latter are, if anything, more 

 thorough going, some of them believing that the j^rotoplasm originally introduced 

 was pre-ordained, or especially endowed with the power to give rise to a countless 

 number of plants and animals quite uncontrolled by external stimuli — the external 

 forces at the most playing a subordinate role, modifying or improving, but never 

 interfering with or determining the line of development. Though it is not alleged 

 that the original protoplasm contained miniatures of all the plants and animals 



THINS. HOT. DDB. SOC, N.S VOL. VII., PART XIII. 3 T> 



