VITALITY—UROLEPTUS MOBILIS 301 
the species named are certainly not confirmed by my results 
with Uroleptus mobilis. Up to the present time I have success- 
fully cultivated thirty-three series, seventeen of which have died 
a natural death, while sixteen are living in various phases of 
vitality. Every one of these series was derived from the con- 
jugation of two closely related individuals, and all came from 
the protoplasm of one single cell, the first individual of the A 
series, which was isolated as an ex-conjugant on November 16, 
1917. In-breeding, therefore, has been close and continuous, 
and we have data to determine whether or not this has been 
a cause of deterioration in protoplasmic vitality of the later 
series. Adopting the relative vitalities of the seventeen. series 
FR Fe F3 Fy Fs Fg By, Fg Fo 
Capea Se es cE Sa Se 
yf TENS we Sei ~XZ2----h 
Le, Q \ Uy ~a----- b----- @----- k 
A series‘< . es Ve 
er: “Upsse Dea Se @seear L 
\ _--N----W----]j ba Ge 
Jer J <4 
Fax 
Diagram 1 
given in table 3 as a vitality index, we may compare the later 
series with the earlier ones, following the different lines one 
by one. Diagram 1 gives a graphic representation of the filial 
series to the ninth generation. 
The two branch lines from the parent A differed widely in 
fecundity; conjugation epidemics were frequent in all representa- 
tives of the branch starting with the C series, but very infrequent 
in representatives of the other branch. In most cases of the 
latter set, conjugations occurred for the first time late in the 
life-cycle, so that all representatives of this branch came from 
relatively old parents. The W series, for example, from N 225 
on May 31, 1919, gave no successful conjugation test for 230 
days, or not until it was 255 generations old, when the 7 series 
was started. The calendar sequence of the origin of the different 
series is given in diagram 2. © 
