74 REPRODUCTION AND LIFE HISTORY’. 
doing, or as dints from external forces. The “body” is 
thus changed, but there is much doubt whether the repro- 
ductive cells within the “body” are affected specifically by 
such changes. Weismann denies the transmissibility of 
any characters except those inherent in the fertilised egg- 
cell, and therefore denies that the influences of function 
and environment are, or have been, of direct importance 
in the evolution of many-celled animals. Such influences 
affect the dody, and produce what are technically called 
““ modifications,” but these modifications do not affect the 
reproductive cells—at least not in a specific representative 
way. Therefore modifications are not likely to be trans- 
mitted, and there seems no good evidence to show that 
they are. Many of the most authoritative biologists are at 
present of this opinion. On the other hand, many still 
maintain that profound changes due to function or environ- 
ment may saturate through the organism, and affect the 
seproductive cells in such a way that the changes or 
modifications in question are in some measure transmitted 
to the next generation. The question remains under dis- 
‘cussion, but the probabilities are strongly against the 
transmissibility of acquired characters. 
It is important to try to distinguish different modes of 
hereditary resemblance. The characters of the two parents 
may be d/ended in the offspring, or those of one parent 
may find predominant expression (exclusive inheritance), or 
the characters of one parent may be expressed in one part 
of the offspring and those of the other parent in another 
(particulate inheritance). 
Another important inquiry is into the share that the 
various ancestors have ox an average in forming any indi- 
vidual inheritance. The inheritance of an animal repro- 
duced in the ordinary way is always dual, partly maternal 
and partly paternal, but ¢zrvovgh the parents there come 
contributions from grandparents, etc. Galton’s Law of 
Ancestral Inheritance states that ‘‘The two parents con- 
tribute between them, on the average, one half of the total 
heritage; the four grandparents, one quarter; the eight 
‘great-grandparents, one eighth, and so on.” 
Another generalisation of great interest is Mendel’s Law, 
which seems to apply to certain cases, ¢.g. peas, stocks, 
