Mutations and Evolution. 
235 
CHAPTER X. 
Inheritance of acquired Characters. 
In the last chapter it was pointed out that adaptational 
recapitulatory characters have apparently not originated directly 
through chromatin variations, but indirectly via the cytoplasm. 
Under the influence of Weismann’s conception of continuity of the 
germplasm, the very possibility of acquired characters or impressed 
modifications being inherited, was denied. Like so many other useful 
biological conceptions this was pushed to an extreme, and a non¬ 
existent degree of isolation and insulation of the germ cells from 
the soma was freely assumed. But in the last decade there has 
been an increasing tendency to adopt a more reasonable attitude to 
these problems. Weismann’s conception of blastogemc and 
somatogenic variations or characters has also tended to lay too 
great emphasis on a distinction which can scarcely be said to exist 
at all in plants, except in sporogenesis, namely the segregation 
between germ cells and somatic cells. The contrast we have 
ventured to draw between karyogenic or nuclear characters and 
organismal or recapitulatory characters, seems more in accord with 
our present knowledge of the development, cytological structure 
and genetic behaviour of organisms. 
In the meantime, experimental evidence for the inheritance of 
acquired characters and related phenomena has been slowly 
accumulating, but space will permit of reference to only a few 
papers. We may first mention Agar’s (1913) work on parallel 
induction in the Daphnid, Simocephalus vetulus, where references to 
the related literature will be found. Agar discovered that 
when Simocephalus is fed on a culture of Protophyta the valves 
of the carapace became reflexed, the degree of this abnormality 
gradually increasing during successive instars or moults. If such 
individuals were removed to normal conditions before their 
(parthenogenetic) eggs were laid, these eggs nevertheless developed 
into adults showing the same abnormality which their parents had 
acquired ontogenetically through environmental impress. But the 
effect soon wore off in later generations grown in normal conditions. 
Similarly, grown at higher temperature the animals were very 
much smaller, developed more rapidly and produced smaller broods. 
Eggs laid shortly after removal to ordinary temperature developed 
into adults nearly as small as their parents, but in P 2 little of the 
effect remained. 
