63G 
GILBEET E. JOHNSON. 
SO low that in the restricted number of generations through 
which the cultures lasted no males were seen at all. In a few 
instances, however, males did occur in the filial generations, 
and in such cases the ratio was sometimes high. The first 
filial generation of culture C, which consisted of 36 males and 
31 females, furnishes a very striking instance of this. 
Potts ( 15 ), in reference to the free-living hermaphrodite 
species which he studied, states that the production of males is 
cyclical, but that there is no rule that they should appear at 
stated intervals or restricting their production to a period or 
periods of maturity. My own cultures did not last long 
enough to enable me to throw light on the question. But, 
as has been already stated, although males are as a rule 
entirely wanting in the filial generations, they always develop 
in a high ratio in the parental generation consisting of larvEe 
taken from the freshly killed worm ; and it is not unreason- 
able to suppose that, had the cultural series lasted over a 
longer period, males would sooner or later have reappeared. 
Potts states that it is not probable that the sex proportions 
are governed by nutrition, and my own results bear out this 
opinion. 
Maupas ( 14 ), in inducing males of llh. elegans (p. 477) 
to re-fertilise hermaphrodites whose stock of sperm was 
exhausted, obtained an enormous increase in the proportion 
of males to females in the offspring, so that the sexes became 
almost numerically balanced. In attempting the same with 
Rh. marionis (p. 506) he did not succeed in affecting the 
ratio at all. 
In the present species re-fertilisation, like ordinary fertili- 
sation, has not been observed, and in those cases of repro- 
duction in which males may nevertheless have taken part the 
sex of the offspring may not have been affected, though, 
curiously enough, the only males produced (besides those of 
the parental generation, which occur regularly among the 
nematodes taken while larval from the worm) have been among 
the offspring resulting from these cases. 
The culture series made in the course of this work were for 
