Ewarr— aration: Germinal and Environmental. 357 
II.— Environmental changes from the end of development to the end of the 
reproductive period, including changes in the germ-cells during 
their growth and maturation. 
(1). Experiments bearing on the question of the inheritance of acquired characters. 
Every plant and animal has a certain amount of plasticity, just as every 
species has certain potentialities. , 
In virtue of this plasticity both plants and animals, by responding to external 
stimuli, are able, during their lifetime, to adapt themselves, within certain 
limits, to their environment. By treating individual plants and animals of the 
same variety differently—no matter how intimately related—surprisingly diverse 
results (difference in size, in the time maturity is reached, fertility, &c.) are 
sometimes obtained, nurture during at least the individual life having, in many 
cases, a wonderful power over nature. Can any of the results of nurture (acquired, 
it may be, at the expense of much time and energy), changes in habit, or in 
structure, in size or colour, in mind or muscle, be handed on even in a modified 
way to the offsprmg? In other words, is it possible, in some incomprehensible 
way, to engraft on the germ-plasm specific somatic changes acquired during the 
life of the individual, ¢.e. to transmute definite environmental somatic variations 
into germinal variations? ‘To this still burning question many, following Darwin, 
would give an affirmative answer, while Weismann and his followers would as 
unhesitatingly reply in the negative. 
Darwin, Spencer, and many others—doubting, apparently, the sufficiency of 
germinal variations, and failing, perhaps, to realize sufficiently the influence of 
the environment on the germ-plasm—imported into the new evolution hypothesis 
some of the old hypotheses generally associated with the name of Lamarck. 
Hence, until Weismann adversely criticised the want of confidence alike of 
prophets and followers in the new doctrines, and insisted on the all-sufficiency 
of congenital (germinal) variation, it was commonly believed that all sorts of 
peculiar mental and physical traits—normal and abnormal—acquired for the 
first time by the parents, could be handed on practically unchanged to their 
offspring. 
I have not yet met with any evidence in support of the belief that specific 
acquired somatic variations are hereditary. On the contrary, many of my 
results indicate that the handing on, even in a highly modified form of definite 
(non-latent) traits acquired during the lifetime, is extremely improbable. 
Some of these results may be worth mentioning. Hitherto tails and horns 
