80 
Transactions Texas Academy of Science. — 1906. 
even over a number of years; that is, it may possess periodic re- 
productive processes. One might object that in such a case repro- 
duction and death are not associated, and that reproduction by germ 
cells seems to be combined with the state of greatest vigor of the 
organism. But even where the organism exhibits periodic repro- 
ductive activity, it has attained at its first reproductive act, even in 
extreme cases of neotenia, a relatively high degree of specialization. 
Definite functions are then to be sure in their state of ultimate per- 
fection, the condition of division of labor at its maximum, and 
somatic energies in general at their fullest development. But the 
ability to become further specialized, which is the power of continu- 
ance of somatic differentiation, has quite or almost reached its limit. 
This goal is assuredly a critical stage for the organism, of cessation 
of constructive growth. And, more particularly, the organism has 
had to pay for this differentiation: it has accumulated in geometri- 
cally increasing amount harmful waste products that it can no 
longer successfully excrete. A little more and senile changes appear, 
in some organisms immediately, in other more gradually. When 
senescence, or what I have preferred to call self-poisoning, sets in* 
more slowly, there is time given for a succession of reproductive 
periods. Therefore in e. g. a mammal which may have one or more 
reproductive periods a year through a number of years the first of 
these periods does not occur at the time of its greatest vitality, for 
even then its anabolic growth energies have begun to decline and self- 
intoxication has arisen. Here, accordingly, just as surely as in an 
insect, though perhaps not so apparently, the first act of generation, 
much more, therefore, the later ones, is a process of escape of germ 
cells from a body that is on the way to death. 
We can agree with the conclusion of Weismann that the germ cells 
are essentially immortal, because they have unlimited powers of re- 
production. But this conclusion does not explain why there should 
take place at particular intervals separation of germ cells from 
body cells, the act we know as sexual reproduction. To state that 
a specialized tissue cell can no longer reproduce the whole individual 
because it has lost determinants of the other parts, is logically per- 
missible, but doe& not explain why tissue cells should not reproduce 
themselves indefinitely. If the determinant hypothesis be correct, 
which is a question apart from our present subject, the presence of 
the full number of determinants in a germ cell does not explain why 
germ cells should separate from the soma. Germ cells are rightly 
said to maintain a perpetual power of multiplication, because they 
remain generalized. But there is an easier and clearer way of com- 
prehending generalization than by the construction of an elaborate 
