1892.] Heredity and the Germ- Cells, 651 
exchange of hereditary substance altogether analogous to that 
observed in the higher multicellular organisms. 
The cultures were made in a drop of water upon a slide, and 
feeding was adapted either to the herbivorous or carnivorous 
habits of the species. Under these conditions it was found 
that the rate of fission or direct multiplication varied directly 
with the temperature and food, rising in some species (Glau- 
coma scintillans) to five bipartitions daily. With the optimum 
of conditions this rate, if sustained for thirty-eight days, would 
produce from a single individual a mass of protoplasm equiv- 
- alent to the volume of the sun. This rate is, however, found 
to be steady for a time, and then the offspring decline into 
“senescence,” in which they appear at times only one-fourth 
the original size, with reduced buccal wreaths and degenerate 
nuclear apparatus. This is reached sooner in some species than 
in others; Stylonichia pustulata survives three hundred and 
sixteen generations or fissions, while Leucophrys patula persists 
to six hundred and sixty generations. Finally, even under 
the most favorable condition of environment, death ensues. 
Not so where conjugation is brought about by mingling the 
offspring of different broods in the same fluid, as in the nat- 
ural state. Maupas soon discovered that exhaustion of food 
would induce conjugation between members of mixed broods. 
He thus could watch every feature of the conjugation process, 
and determine all the phases in the cycle of life. These dif- 
fered, as in the longevity of the species. In Stylonichia, for 
example, “immaturity” extended over the first one hundred 
bipartitions ; “puberty,” or the earliest phase favorable to 
conjugation, set in with the one hundred and thirtieth bipar- 
tition; “eugamy,” or the most favorable conjugation phase, 
extended to the one hundred and seventieth; then “senes- 
cence” set in, characterized by a sexual hyperzsthesia in 
which conjugation was void of result or rejuvenescence, owing 
apparently to the destruction of the essential nuclear appara- 
tus. 
Conjugation begins with the approach of two individuals, 
and adhesion by their oral surfaces. There is no fusion, but 
an immediate transformation in the cell contents of each indi- 
46 
