Life History of Nereis grubei — Schroeder 
group. It is felt that these data provide concrete 
evidence in support of the projected swarming 
groups. 
A line has also been drawn connecting the 
largest oocytes found in each collection before 
the first swarm in February. The oldest animals 
in each of these collections ought to be those 
destined to participate in the first swarm and 
should therefore represent a single swarming 
group. This line was used to estimate roughly 
the growth rate of the oocytes during each phase 
and to localize the size range during which the 
growth rate increases. The line suggests an 
oocyte growth rate of about 1.8p/day during the 
second, rapid phase. Oocyte growth rates were 
also determined for 14 animals with oocytes 
over lOOp in diameter maintained in the lab- 
boratory, as mentioned above. These indicated a 
growth rate of 1.74d=0.49p/day. This growth 
rate estimate is also supported by data from a 
single unfed animal which was brought into the 
laboratory with 111-p oocytes. It swarmed 62 
days later. Assuming a final oocyte diameter of 
200p, the oocytes in this individual must have 
grown at a rate of about 1.4p/day. The average 
growth rate, during the final period of rapid 
growth, is thus between 1.6 and 1.7p/day. The 
growth rate may not be constant throughout the 
period of rapid growth in N. grubei, and a defi- 
nite slowing down of growth as the maximum 
size is approached has been reported for N. 
diversicolor (Clark and Ruston, 1963). 
The first swarming takes place in February, 
and evidence has been found for a swarm each 
month until June. Each swarm seems to involve 
fewer animals than the one preceding it, so that 
the bulk of the population swarms in February 
and March. In February virtually all the ma- 
turing animals in the Egregia holdfast habitat 
disappear; subsequent swarms arise from the 
Gastroclonium. This fact accounts for the lack 
of data for the spring of 1965. Collections were 
made during this period, but only from the 
holdfasts, which were almost totally devoid of 
maturing animals. After the discovery of N. 
grubei beneath Gastroclonium, both habitats 
were monitored during the spring of 1966. 
Again mature animals disappeared suddenly and 
almost completely from the Egregia holdfasts 
during February. However, a significant popu- 
lation remained beneath the Gastroclonium 
479 
from which at least a few animals swarmed 
monthly until June. 
One of the swarms (represented in Figure 1 
by the heavy dotted line over May 1966) has 
been inferred from the fact that two animals 
taken from the field on April 26 swarmed si- 
multaneously in the laboratory on May 19. A 
search of the Gastroclonium on May 22 failed 
to reveal any metamorphosing animals; this is 
what would be expected if the animals in the 
laboratory had swarmed simultaneously with a 
group in the field. 
The dates of the full moon for several months 
of breeding activity during the winter of 1965- 
1966 have been indicated by vertical dotted 
bands in Figure 1, since nereid breeding ac- 
tivity has often been correlated with the phase 
of the moon (Korringa, 1947 ; Hauenschild, 
1966). It should be recalled that the observa- 
tion of metamorphosing animals in the field 
must antedate the swarming of these same ani- 
mals, so that the swarming dates indicated in 
Figure 1 are all somewhat early. Furthermore, 
the theory of Hauenschild (1966) suggests 
that the moon phase might correlate at the point 
where the oocyte growth rate increases rather 
than at the time of actual swarming. It is not 
known whether a latent period occurs between 
the supposed lunar stimulus and the observed 
response; the figures presented, do not, in my 
opinion, either affirm or deny a possible phase- 
setting relationship with the lunar cycle. The 
fact that subgroups are separable within the 
population in early December suggests that 
some determination of the spawning groups has 
occurred before the time that the oocyte growth 
rate has increased within any group. This adds a 
third point in time for the possible intervention 
of environmental stimuli in determining the 
breeding periodicity (see discussion by Clark, 
1965). 
COMPARISON WITH A SOUTHERN CALIFORNIAN 
POPULATION 
At the outset of this work a definite breeding 
season had not been expected, since Reish 
(1954£) reported that the population at Point 
Fermin showed continual reproduction through- 
out the year, and that specimens in some stage 
of metamorphosis could be taken at any time. 
