Brachyura and Anomura of Puget Sound — KNUDSEN 
15 
another were simply grouped into that size class. 
Figure 5 shows the distribution of those females 
with and without eggs. It will be noted that the 
12 and 13 mm size range contained the largest 
number of reproductive and nonreproductive 
females, and that the total number of individuals 
drastically drops off on either end of the curve. 
It will be noted that the two curves are amaz- 
ingly similar, indicating that egg deposition does 
not necessarily occur earlier in larger or smaller 
size classes, but that the period of deposition is 
irrespective of size class and is determined solely 
by the season itself. 
PRODUCTIVITY: Egg counts were made for 42 
specimens of H. oregonensis. The number of 
eggs ranged from around 800 to over 11,000 per 
brood. The average for the 42 specimens was 
4,500 eggs per brood. When the number of 
eggs is plotted against the width of the carapace, 
it can be seen that the number of eggs increases 
in almost a straight line until a size class of 
12.5 mm is reached. At this time the line breaks, 
indicating that the number of eggs produced 
actually increases above the expected rate of 
production for the smaller animals, as the cara- 
pace size increases. As many as 22,000 eggs 
could be produced in a single year by some of 
the largest females which produce two broods. 
For those females that have two broods a year 
the average production would be about 9,000. 
However, since only about 70% actually pro- 
duce the second brood, on the basis of 100 
Fig. 5. Distribution of female Hemigrapsus oregon- 
ensis, with or without eggs attached to the pleopods, 
when plotted by size class. 
individuals a yearly average of 7,650 would be 
obtained. This latter figure is probably more 
accurate for the population as a whole and is 
used to denote annual production. 
LARVAL DEVELOPMENT: The larval develop- 
ment of this species has been worked out by 
Hart (1935:430-432), using specimens taken 
from Vancouver Island, British Columbia, which 
is close to the latitude of our own studies. She 
lists the time required for development to the 
first crab stage in two individuals as being 4 and 
5 weeks. If the southern Puget Sound specimens 
develop at a similar rate, the first crab stages 
could reach the beach in the early weeks of 
June and continue to arrive into October. Hart 
has completely illustrated the larval stages of 
H. nudus and has given sufficient data on H. 
oregonensis, so that those extremely similar 
larvae may be separated when taken in plankton. 
POSSIBLE TRIGGER MECHANISMS 
In a study of trigger mechanisms which may 
initiate the reproductive processes, several pos- 
sibilities must be considered: is the reproduc- 
tive life cycle triggered at its very beginning, 
in the species being studied, and then do all 
subsequent events simply follow suit as in a 
chain reaction? Or does each individual event 
such as oogenesis, copulation, egg deposition, 
etc., have its own individual triggering device? 
A review of the literature has shown that most 
generally photo-period, temperature, or a com- 
bination of both serve as triggering mechanisms 
for reproductive activity amongst the inverte- 
brates and many of the vertebrates. Since a 
parallel, though sometimes lagging, physiological 
cycle progresses almost concurrently with the 
annual cycle of external stimuli, a study of 
trigger mechanisms must eventually include a 
careful study of hormone and other physiological 
activities. Although many experiments were at- 
tempted in our research, none produced results 
of sufficient magnitude to warrant in this paper 
a review of the literature concerning trigger 
mechanisms, or an exhaustive description of 
experimentation. Experiments were set up dur- 
ing several parts of the year where temperature 
and photo-period were either increased, de- 
creased, or maintained at a steady state, either 
simultaneously or independently, and the species 
