.] 89 
[Hyatt. 
evolution of the cycle can only be pursued successfully by workers 
in phylogeny. 
Heretofore the transmission of similar characteristics and ten- 
dencies has been supposed to be confined necessarily to those that 
appenred before the expiration of the reproductive period in the 
individual. This doctrine is not supported by the facts that form 
the basis of bioplastology, since the repetition of similar charac- 
teristics also takes place in the decline of life, and senile character- 
istics are as clearly parallel in different individuals, species, 
genera, and so on, as in their young. Tt nuist be remembered, 
also, that this assumption utterly disregards heredity, as exhibited 
in the propagation of characteristics in organic rejtroduction 
by fission of autotemnons- 
Characteristies of organs and of jiarts are, with certain exce|i- 
tions, based upon inci-ements of l)ulk during the progressive 
stages of <levelo]>ment, and consequently to a certain extent gen- 
etic energy, which controls these or directs them into parallel lines 
of reproduction, can ideally, at least, be separated from growth 
force. When the extreme of old age is reached and absolute 
decrease in bulk takes place, together with the disappearance of 
characteristics which have been elaborated i)reviousl3'-, there is no 
cessation of the reproduction of simihir characteristics. The 
manifestations of the working of genetic energy, or that energy 
Avhich holds the type true to its own breed through parallel develop- 
ment, are just as powerful on the verge of natural decease, and 
even more marked in some respects, than during the adult period. 
In the young hereditary similarities derived from more or less 
remote ancestors are lepeated, but these are more and more over- 
grown and replaced by more recently acquired characteristics as 
the ndult period is approached. In old age these more recently 
acquired characteristics disappear, and in consequence of their 
disappearance, certain parts of the body and finally the whole 
body assamj aspects which can be more or less closely compared 
with those of the same parts and of the entire body in the young 
before the differential characteristics of the adolescent and adult 
periods arose. 
If now one compares different individuals of the same species, 
it is easily seen that their younger stages of development are 
identical, and that they diverge as they grow older until the adult 
