ON REPRODUCTION, ANIMAL LIFE CYCLES 
AND THE BIOGRAPHICAL UNIT . 1 
DR. THOS. H. MONTGOMERY, JR . 2 
A. Reproduction as an act of excretion by the offspring. 
As the term is most broadly used, we mean by race a temporal 
succession of individuals. The termination of a race is probably not 
a function of any of its inherent qualities, but rather one of the ex- 
ternal conditions in which it is placed, provided its constituent indi- 
viduals continue their power of reproduction. That is, environmental 
conditions remaining* favorable, and individuals continuing to pro- 
create, a race should last indefinitely. 
But individuals do not persist indefinitely, they meet with the dis- 
solution that we know as death, or at least always some portion of 
them finds this end. The race continues simply because individuals 
before their death reproduce themselves. There may then be a direct 
causal connection between death and reproduction; and, as we shall 
try to show, reproduction takes place because there is death but need 
not be the cause of it. 
Reproduction has been defined as growth beyond the normal mass. 
But this is not a valid statement, for reproduction is a regular and 
not an abnormal process and need not embody increase in mass. 
Mechanically it is the power of multiplication by division. Physio- 
logically it is in part at least the action of the escape of a part from 
an empoisoned mass, as becomes evident when we compare its different 
forms. 
The Protozoa afford three main kinds of reproduction, and they 
intergrade: sporulation, budding and fission. The first is that pro- 
cess where the Protozoan after repeated simultaneous or successive 
nuclear divisions breaks into numerous parts that separate from 
each other, leaving behind them a residual lifeless mass. Hitherto 
no particular importance seems to have been ascribed to this residuum, 
no importance in the nature of a probable cause at least, though it 
would seem to be demonstrated that a residuum is always left behind 
in such division. Yet most patently sporulation is the separation of 
individuals from a part that is inert and moribund. The residuum 
Contributions from the Zoological Laboratory of The University of Texas, 
No. 82. 
* 2 Professor of Zoology, The University of Texas. 
