Hyatt.] 74 [Aprils. 
It does not oblige the student to assume with Weismann an 
immortal germ plasm and a mortal somatoplasm in the body, the 
former alone ca})able of transmitting characteristics but prevented 
from acquiring them, the latter capable of acquiring them to any 
extent but not able to transmit them. This paradox can only 
be accounted for by suj)posing organic differentiations between 
germ plasm and tissue plasm which cannot be demonstrated and are 
in direct contrast to the statements of the morphic nniformit}' of 
young cells in structure, aspect, and origin. Such vast differen- 
tiation Avould be accompanied in Metazoa by some traceable change 
of structure taking place very early in the embryo when growth 
force Avas at its maximum ; but there is nothing of this sort. The 
reproductive cells are not ripe until, like other tissue cells, they 
have passed through certain stages of development. The immor- 
tals behave, in other words, just like mortals while growing up, and 
in old age they and their carriers, the generative organs, suffer from 
degeneration as a rule before many of the other tissues give way. 
In fact the so-called immortals are shorter lived in the individual 
so far as their functional efficiency is concerned than their mortal 
brethren . 
The mnemonic theory is perfectly consistent and adds strength 
to Spencer's theory of heredity, which makes no assumption of 
gemmules or distinct organic peculiarities that cannot be tested 
by observation. This theory is as follows: "That changes of 
structure caused by changes of action, must also be transmitted, 
however obscurely, from one generation to another, appears to be 
a deduction from first principles — or if not a specific deduction, 
still, a general implication. For if an organism A, has, by any 
peculiar habit or condition of life, been modified into the form A', 
it follows inevitably, that all the functions of A', reproductive 
function included, must be in some degree different from the 
functions of A. An organism being a combination of rhythmically- 
acting parts in moving equilibrium, it is impossible to alter the 
action and structure of any one part, without causing alterations 
of action and structure in all the rest ; just as no member of the 
Solar System could be modified in motion or mass, without pro- 
ducing re-arrangements throughout the whole Solar System. And 
if the organism A when changed to A' must be changed in all its 
functions ; then the offspring of A' cannot be the same as they 
