118 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
The riddle was, in part at least, solved by a long series of careful 
observations. In November 1885, M. Maupas isolated an Infusorian 
(Stylonichia pustulata), and observed its generations till March 1886, 
By that time there had been two hundred and fifteen generations pro- 
duced by ordinary division, and since these lowly organisms do not 
conjugate with near relatives, there had been no conjugation. 
What was the result? At the date referred to, the family was 
observed to have exhausted itself. The members were being born old 
and debilitated. The asexual division came to a standstill, and the 
powers of nutrition were lost. 
Meanwhile, before the generations had exhausted themselves, several 
of the individuals had been restored to their natural conditions, where 
they conjugated with unrelated forms of the same species. One of 
these was again isolated, and watched for five months. In this case, 
up till the one hundred and thirtieth generation, it was found that on 
removal to fresh conditions the organisms were capable of conjugating 
with unrelated forms. Later this power was lost, and at the one 
hundred and eightieth generation the individuals of the same family 
were observed making vain attempts to conjugate with each 
other. j 
We thus see that without normal conjugation the whole family 
becomes senile, degenerates both morphologicaliy and physiologically. 
Morphologically, the individuals decrease in size, until they measure 
only a quarter of their original proportions, the micronucleus atrophies 
completely or partially, the chromatin of the macronucleus gradually 
disappears, other internal structures also degenerate. Physiologically, 
the powers of nutrition, division, and conjugation come to a standstill, 
and this senile decay of the isolated individuals or family inevitably 
ends in death. 
The general conclusion is evident. Sexual union in those Infusorians, 
dangerous, perhaps, for the individual life, and a loss of time so far as 
immediate multiplication is concerned, is absolutely necessary for the 
species. The life runs in strictly limited cycles of asexual division. 
Conjugation with allied forms must occur, else the whole life ebbs. 
Without it, the Protozoa, which some have called ‘‘immortal,” die a 
natural death. Conjugation is the necessary condition of their eternal 
youth. 
It must be noted, however, that some subsequent investigators have 
watched over two hundred asexual generations of ciliated Infusorians 
without seeing the slightest trace of senile degeneration. Calkins has 
cultivated Paramecium for over six hundred generations without 
conjugation by giving beef extract when degeneration threatened to set 
in. The same result was obtained by stimulating with alcohol, 
strychnine, etc. 
Ecology. — Many Protozoa raise organic débris once more 
into the circle of life, and many form part of the food 
of higher animals. Thus those pelagic Foraminifera and 
Radiolarians, which sink dying to the great oceanic depths, 
form along with more substantial débris the fundamental 
